usb: gadget: add multiple definition guards

If f_fs.c and u_serial.c are combined together using #include, which has
been a common practice so far, the pr_vdebug macro is defined multiple
times. Define it only once.

Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/u_serial.c

@@ -132,11 +132,15 @@ static unsigned	n_ports;
 
 
 #ifdef VERBOSE_DEBUG
+#ifndef pr_vdebug
 #define pr_vdebug(fmt, arg...) \
 	pr_debug(fmt, ##arg)
+#endif /* pr_vdebug */
 #else
+#ifndef pr_vdebig
 #define pr_vdebug(fmt, arg...) \
 	({ if (0) pr_debug(fmt, ##arg); })
+#endif /* pr_vdebug */
 #endif
 
 /*-------------------------------------------------------------------------*/