bcm53xx: fix early serial console

This device actually has a 8250 serial with a shift of 0.
Tested this on a BCM4708.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42538 3c298f89-4303-0410-b956-a3cf2f4a3e73