usb: gadget: increase the notification packet max size

LGE host driver's notification packet max size is 16.
We need to increase max packet size to 16 from 10.

Change-Id: I8a1f8b731b92bddc52c43d32792822246c7e0885
diff --git a/drivers/usb/gadget/f_serial.c b/drivers/usb/gadget/f_serial.c
index 7b6acc6..6fb2ce5 100644
--- a/drivers/usb/gadget/f_serial.c
+++ b/drivers/usb/gadget/f_serial.c
@@ -93,7 +93,7 @@
 	return container_of(p, struct f_gser, port);
 }
 #define GS_LOG2_NOTIFY_INTERVAL		5	/* 1 << 5 == 32 msec */
-#define GS_NOTIFY_MAXPACKET		10	/* notification + 2 bytes */
+#define GS_NOTIFY_MAXPACKET		16
 #endif
 /*-------------------------------------------------------------------------*/