drm/amdkfd: Fix potential deallocation of previously deallocated memory.

Pointer mqd_mem_obj can be deallocated in kfd_gtt_sa_allocate().
The function then returns non-zero value, which causes the second deallocation.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: d1f8f0d1 ("drm/amdkfd: Move non-sdma mqd allocation out of init_mqd")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>