broadcom-diag: remove BUFFALO_UNKNOWN

This was itriggered by to many non buffalo devices

This closes #14043.

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


git-svn-id: svn://svn.openwrt.org/openwrt@37804 3c298f89-4303-0410-b956-a3cf2f4a3e73