drm/amdgpu_vm: fix boolean expressions

Fix boolean expressions by using logical AND operator '&&'
instead of bitwise operator '&'.

This issue was detected with the help of Coccinelle.

Fixes: 9a4b7d4c ("drm/amdgpu: Add vm context module param")
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>