kernel: b53: fix build with brcm47xx

The position of the nvram header file on brcm47xx changed with kernel 
version 4.1.

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


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46170 3c298f89-4303-0410-b956-a3cf2f4a3e73