net/mlx5: fix crash when configure is not called

net/mlx5: fix crash when configure is not called

Although uncommon, applications may destroy a device immediately after
probing it without going through dev_configure() first.

This patch addresses a crash which occurs when mlx5_dev_close() calls
mlx5_mr_release() due to an uninitialized entry in the private structure.

Fixes: 974f1e7ef146 ("net/mlx5: add new memory region support")
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>