Currently pointer pdd is being dereferenced when assigning pointer
dpm and then pdd is being null checked.  Fix this by checking if
pdd is null before the dereference of pdd occurs.

Addresses-Coverity: ("Dereference before null check")
Fixes: 32cb59f3 ("drm/amdkfd: Track SDMA utilization per process")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Reviewed-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>