drm/xe/vm: Fix an error path

If using the VM_BIND_OP_UNMAP_ALL without any bound vmas for the
vm, we will end up dereferencing an uninitialized variable and leak a
bo lock. Fix this.

v2:
- Updated commit message (Lucas De Marchi)
Reported-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Closes: https://lore.kernel.org/intel-xe/jrwua7ckbiozfcaodx4gg2h4taiuxs53j5zlpf3qzvyhyiyl2d@pbs3plurokrj/Suggested-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Fixes: b06d47be ("drm/xe: Port Xe to GPUVA")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222175904.16732-1-thomas.hellstrom@linux.intel.com
(cherry picked from commit 9d0c1c56)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

drivers/gpu/drm/xe/xe_vm.c

@@ -2063,9 +2063,11 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_bo *bo,
 		if (err)
 			return ERR_PTR(err);
 
-		vm_bo = drm_gpuvm_bo_find(&vm->gpuvm, obj);
-		if (!vm_bo)
-			break;
+		vm_bo = drm_gpuvm_bo_obtain(&vm->gpuvm, obj);
+		if (IS_ERR(vm_bo)) {
+			xe_bo_unlock(bo);
+			return ERR_CAST(vm_bo);
+		}
 
 		ops = drm_gpuvm_bo_unmap_ops_create(vm_bo);
 		drm_gpuvm_bo_put(vm_bo);