staging: brcm80211: fix off-by-one error in swap functions

The original implementation iterated over the data in buf+1 through buf+size,
whereas it should have been over the data in buf through buf+size-1.

Tested on Mac G5 PPC and BCM63281.

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Tested-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>