USB: gadget: g_serial: INF file updated

Updated the INF file for g_serial gadget.  It should work with
most recent Windows systems now.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>