staging: brcm80211: fix checkpatch issue introduced in wlc_alloc.c

Patch "[59807ce] local used function made static" introduced a new
checkpatch warning which is fixed with this patch.

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Reviewed-by: Roland Vossen <rvossen@broadcoom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>