CACHE: net: asix: Fix asix driver to work with data cache on

The asix driver did not align buffers, therefore it didn't work
with data cache enabled. Fix this.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@gmail.com>