tests: portability cmsis_rtosv2: Fix buffer aligment

The kernel requires the buffer to be word aligned.
Instead of assuming the word size is 32bits,
lets align the buffer to the size of a pointer,
which should match the word size (and which
is the check the kernel performs).

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

tests/subsys/portability/cmsis_rtos_v2/src/mempool.c

@@ -16,7 +16,7 @@ struct mem_block {
 	int member2;
 };
 
-static char __aligned(4) sample_mem[sizeof(struct mem_block) * MAX_BLOCKS];
+static char __aligned(sizeof(void *)) sample_mem[sizeof(struct mem_block) * MAX_BLOCKS];
 static const osMemoryPoolAttr_t mp_attrs = {
 	.name = "TestMempool",
 	.attr_bits = 0,