operator.pos(ums_ndarray) is always an identity (#783)

Since dpnp.positive is not implemented, to unblock integration testing
implemented __pos__ to return self.

Author: oleksandr-pavlyk

dpctl/tensor/_usmarray.pyx

@@ -857,7 +857,7 @@ cdef class usm_ndarray:
         return NotImplemented
 
     def __pos__(self):
-        return _dispatch_unary_elementwise(self, "positive")
+        return self  # _dispatch_unary_elementwise(self, "positive")
 
     def __pow__(first, other, mod):
         "See comment in __add__"