ixgbe: Remember to write ixfi changes after modifying

This patch corrects a bug in ixgbe_setup_ixfi_x550em where we were
reading and modifying IXGBE_KRM_LINK_CTRL_1 but forgot to write the
results back.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>