staging: brcm80211: cosmetic changes

Code cleanup. Added lock related comments to wl_mac80211.c. Also removed a
redundant function definition.

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