smsc95xx: Fix MAC address programming

Commit 79ad5440 broke MAC address
programming in the SMSC95xx register set.

Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Wolfgang Grandegger <wg@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Simon Glass <sjg@chromium.org>