ixgbe: fix endianess when writing driver version to firmware

This patch makes sure that register writes are in little endian and
also converts the reads back to big-endian.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>