net/mlx5: fix memory region cleanup

net/mlx5: fix memory region cleanup

mlx5 driver has a global list of Memory Regions created by
device, and there is a ml5_mr_release() routine which makes
a memory cleanup at device closing. The head of device MR list
was fetched outside the rwlock protected section. Also some
noticed typos are fixed.

Fixes: 974f1e7ef146 ("net/mlx5: add new memory region support")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>