[PATCH] USB Gadget: fix g_serial debug module parm

g_serial.ko can't be load as module because "debug" is only
defined if G_SERIAL_DEBUG is defined, but "debug" is referenced
in MODULE_PARM().

drivers/usb/gadget/serial.c

@@ -157,8 +157,12 @@ do {									\
 
 /* debug macro */
 #if G_SERIAL_DEBUG
-
 static int debug = G_SERIAL_DEBUG;
+#else
+static int debug = 0;
+#endif
+
+#if G_SERIAL_DEBUG
 
 #define gs_debug(format, arg...) \
 	do { if (debug) printk(KERN_DEBUG format, ## arg); } while(0)