drm/amdkfd: Fix leak in dmabuf import

drm/amdkfd: Fix leak in dmabuf import

BugLink: https://bugs.launchpad.net/bugs/1910822
[ Upstream commit c897934da15f182ce99536007f8ef61c4748c07e ]

Release dmabuf reference before returning from kfd_ioctl_import_dmabuf.
amdgpu_amdkfd_gpuvm_import_dmabuf takes a reference to the underlying
GEM BO and doesn't keep the reference to the dmabuf wrapper.

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>