drm/amdgpu: Fix an error code in kfd_mem_attach_dmabuf()

If amdgpu_gem_prime_export() fails, then this code accidentally
returns zero/success instead of a negative error code.

Fixes: 5ac3c3e4 ("drm/amdgpu: Add DMA mapping of GTT BOs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c

@@ -639,14 +639,16 @@ kfd_mem_attach_dmabuf(struct amdgpu_device *adev, struct kgd_mem *mem,
 		      struct amdgpu_bo **bo)
 {
 	struct drm_gem_object *gobj;
+	int ret;
 
 	if (!mem->dmabuf) {
 		mem->dmabuf = amdgpu_gem_prime_export(&mem->bo->tbo.base,
 			mem->alloc_flags & KFD_IOC_ALLOC_MEM_FLAGS_WRITABLE ?
 				DRM_RDWR : 0);
 		if (IS_ERR(mem->dmabuf)) {
+			ret = PTR_ERR(mem->dmabuf);
 			mem->dmabuf = NULL;
-			return PTR_ERR(mem->dmabuf);
+			return ret;
 		}
 	}