RDMA: Fix dependencies for rdma_user_mmap_io

RDMA: Fix dependencies for rdma_user_mmap_io

The mlx4 driver produces a link error when it is configured
as built-in while CONFIG_INFINIBAND_USER_ACCESS is set to =m:

drivers/infiniband/hw/mlx4/main.o: In function `mlx4_ib_mmap':
main.c:(.text+0x1af4): undefined reference to `rdma_user_mmap_io'

The same function is called from mlx5, which already has a
dependency to ensure we can call it, and from hns, which
appears to suffer from the same problem.

This adds the same dependency that mlx5 uses to the other two.

Fixes: adbfc6188d3b ("RDMA/hns: Use rdma_user_mmap_io")
Fixes: 3e6c2fc63164 ("RDMA/mlx4: Use rdma_user_mmap_io")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>