video via: fix iomem access

This driver is not respecting the iomem memory space restrictions
and does direct access. This works on x86 but is non-portable and
should not be done.  Converted memcpy() of 2 to readw.
Last post increment of romptr was unnecessary since pointer never
used after that.

Found by sparse, compile tested only.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>