ssb: pci: Fix flipping of MAC address

Since commit e5652756 entitled "ssb: pci: Standardize a function to get mac
address", the SPROM readout of the MAC has had the values flipped so that
00:11:22:33:44:55 became 11:00:33:22:55:44. The fix has been tested on both
little- and big-endian architectures.

Reported-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>