net/mlx4_en: mlx4_en_verify_params() can be static

Fix static error introduced by commit:
b97b33a3 [645/653] net/mlx4_en: Verify
mlx4_en module parameters

sparse warnings:
drivers/net/ethernet/mellanox/mlx4/en_main.c:335:6: sparse: symbol
'mlx4_en_verify_params' was not declared. Should it be static?

CC: netdev@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>