net/mlx4_en: fix spelling mistake: "quiting" -> "quitting"

There is a spelling mistake in a en_err error message. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>