Reword logic in copy_from_device

In deciding where a copy from device could be done using a direct
call to memcpy, we queried usm type of the source allocation with
respect to the context to which the destination allocation was
bound.

The test was assuming that any answer other than 'unknown' indicated
that the USM allocation was known and a memcpy could be called.

This did not work well when destination was a host device. For example,
this crashed:

```
SYCL_ENABLE_HOST_DEVICE=1 python -m pytest dpctl/tests/test_usm_ndarray_ctor.py::test_to_device
```

It passes now.

Author: oleksandr-pavlyk

dpctl/memory/_memory.pyx

@@ -33,6 +33,7 @@ from dpctl._backend cimport (  # noqa: E211
     DPCTLaligned_alloc_device,
     DPCTLaligned_alloc_host,
     DPCTLaligned_alloc_shared,
+    DPCTLContext_AreEq,
     DPCTLContext_Delete,
     DPCTLDevice_Copy,
     DPCTLEvent_Delete,
@@ -422,8 +423,10 @@ cdef class _Memory:
         the memory of the instance
         """
         cdef _USMBufferData src_buf
-        cdef const char* kind
         cdef DPCTLSyclEventRef ERef = NULL
+        cdef bint same_contexts = False
+        cdef SyclQueue this_queue = None
+        cdef SyclQueue src_queue = None
 
         if not hasattr(sycl_usm_ary, '__sycl_usm_array_interface__'):
             raise ValueError(
@@ -439,23 +442,28 @@ cdef class _Memory:
                     "Source object is too large to "
                     "be accommondated in {} bytes buffer".format(self.nbytes)
                 )
-            kind = DPCTLUSM_GetPointerType(
-                src_buf.p, self.queue.get_sycl_context().get_context_ref())
-            if (kind == b'unknown'):
-                copy_via_host(
-                    <void *>self.memory_ptr, self.queue,  # dest
-                    <void *>src_buf.p, src_buf.queue,     # src
-                    <size_t>src_buf.nbytes
+
+            src_queue = src_buf.queue
+            this_queue = self.queue
+            same_contexts = DPCTLContext_AreEq(
+                src_queue.get_sycl_context().get_context_ref(),
+                this_queue.get_sycl_context().get_context_ref()
                 )
-            else:
+            if (same_contexts):
                 ERef = DPCTLQueue_Memcpy(
-                    self.queue.get_queue_ref(),
+                    this_queue.get_queue_ref(),
                     <void *>self.memory_ptr,
                     <void *>src_buf.p,
                     <size_t>src_buf.nbytes
                 )
                 DPCTLEvent_Wait(ERef)
                 DPCTLEvent_Delete(ERef)
+            else:
+                copy_via_host(
+                    <void *>self.memory_ptr, this_queue,  # dest
+                    <void *>src_buf.p, src_queue,     # src
+                    <size_t>src_buf.nbytes
+                )
         else:
             raise TypeError