IB/mlx5: avoid destroying a NULL mr in reg_user_mr error flow

The mlx5_ib_reg_user_mr() function will attempt to call clean_mr() in
its error flow even though there is never a case where the error flow
occurs with a valid MR pointer to destroy.

Remove the clean_mr() call and the incorrect comment above it.

Fixes: b4cfe447d47b ("IB/mlx5: Implement on demand paging by adding
support for MMU notifiers")
Cc: Eli Cohen <eli@mellanox.com>
Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/mr.c

@@ -1114,19 +1114,7 @@ struct ib_mr *mlx5_ib_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 	return &mr->ibmr;
 
 error:
-	/*
-	 * Destroy the umem *before* destroying the MR, to ensure we
-	 * will not have any in-flight notifiers when destroying the
-	 * MR.
-	 *
-	 * As the MR is completely invalid to begin with, and this
-	 * error path is only taken if we can't push the mr entry into
-	 * the pagefault tree, this is safe.
-	 */
-
 	ib_umem_release(umem);
-	/* Kill the MR, and return an error code. */
-	clean_mr(mr);
 	return ERR_PTR(err);
 }