drm/amdkfd: Remove redundant kfd2kgd interface lookup

kfd_pasid.c isn't using the kfd2kgd interface any more. Remove redundant
code trying to look up a device for finding that interface.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>