staging: wilc1000: fix line over 80 chars in wilc_wlan_txq_filter_dup_tcp_ack()

Fix "line over 80 characters" issue reported by checkpatch.pl.
Use temporary variable to avoid checkpatch.pl issue.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>