amd/amdkfd: fix a kfd_process ref leak

This patch is to fix a kfd_prcess ref leak.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>