net/mlx5e: Remove unneeded io-mapping.h #include

The mlx5 net files don't use io_mapping functionalities. So there is no
point in including <linux/io-mapping.h>.
Remove it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>