kernel: b53: detect revision of BCM5325

The revision is stored in a different register than it is in other 
Broadcom switches.

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


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37995 3c298f89-4303-0410-b956-a3cf2f4a3e73