staging: brcm80211: Removed invalid comment in receive processing.

Comment was a left over from a driver that handled AMPDU aggregation itself (instead
of relying on Mac80211).

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