usb: gadget: u_serial.h: increase MAX_U_SERIAL_PORTS to 8

Mediatek's LTE modem needs up to 8 ports to connect to PC for logging
and debugging under some scenarios. Hence we suggest to increase the
definition of MAX_U_SERIAL_PORTS to 8 for some complex embedded systems.
Signed-off-by: NMacpaul Lin <macpaul.lin@mediatek.com>
Link: https://lore.kernel.org/r/1592286977-30483-1-git-send-email-macpaul.lin@mediatek.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_serial.h

@@ -12,7 +12,7 @@
 #include <linux/usb/composite.h>
 #include <linux/usb/cdc.h>
 
-#define MAX_U_SERIAL_PORTS	4
+#define MAX_U_SERIAL_PORTS	8
 
 struct f_serial_opts {
 	struct usb_function_instance func_inst;