staging: brcm80211: fix checkpatch issue in wlc_channel.c

Patch "[ba84f65] make function definitions and prototype consistent"
introduced a checkpatch warning which is fixed.

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>