drm/amdgpu: Fix a deadlock if previous GEM object allocation fails

Fall through to handle the error instead of return.

Fixes: f8aab604 ("drm/amdgpu: Initialise drm_gem_object_funcs for imported BOs")
Cc: stable@vger.kernel.org
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>