mac80211: b43: fix prefix for config options

Config options in backports are starting with CPTCFG and not with CONFIG_.
CONFIG_B43_BCMA was never true.

This closes #13883.

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


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38385 3c298f89-4303-0410-b956-a3cf2f4a3e73