usb: gadget: g_dnl: hold maximum string descriptor

A USB String descriptor can be up to 255 characters long and it's not
NULL terminated according to the USB spec. This means our
MAX_STRING_SERIAL should be 256 (to cope with NULL terminator).

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/g_dnl.c

@@ -36,7 +36,7 @@
 #define STRING_USBDOWN 2
 /* Index of String serial */
 #define STRING_SERIAL  3
-#define MAX_STRING_SERIAL	32
+#define MAX_STRING_SERIAL	256
 /* Number of supported configurations */
 #define CONFIGURATION_NUMBER 1