Revert "staging: brcm80211: assure common sources are truly common"

This reverts commit ead1256410cb5a79fd3615ba70ba56779c5d21e2 as it
broke the build when building with multiple threads at the same time.

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