staging: brcm80211: assure common sources are truly common

Common code for brcm80211 drivers was resulting in different compiled
object files for the drivers due to compilation flags. This has been
aligned so that they are resulting in same object files. Kconfig now
allows both drivers to be build simultaneously.

Reviewed-by: Brett Rudley <brudley@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>