IB/mlx5: Use u64 for UMR length

The fast_registration length is used to convey length for memory
registrations through UMR which can be of any size up to 2^64.

Change the length type to be u64.

Fixes: 968e78d ('IB/mlx5: Enhance UMR support to allow partial page table update')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/mlx5_ib.h

@@ -420,7 +420,7 @@ struct mlx5_umr_wr {
 	struct ib_pd		       *pd;
 	unsigned int			page_shift;
 	unsigned int			npages;
-	u32				length;
+	u64				length;
 	int				access_flags;
 	u32				mkey;
 };