ice: fix MAC write command

The manage MAC write command was implemented in an overly complex way
that actually didn't work, as it wasn't symmetric to the manage MAC
read command, and was feeding bytes out of order to the firmware. Fix
the implementation by just using a simple array to represent the MAC
address when it is being written via firmware command.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>