drm/amdkfd: fix bug when initializing sdma vm

A logical AND operation was used during mask and shift, instead of a
bitwise AND operation. This patch fixes this bug by changing the
operation to bitwise AND.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>