usb: dwc2: add printf attribute to cat_printf()

As cat_printf() uses printf format strings in its parameters, adding
__printf attribute allows the compiler to detect at compile-time some
errors related to format strings (with -Wformat warning flag).

Signed-off-by: Nicolas Iooss <[e-mail]>
Acked-by: John Youn <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/dwc2/hcd_queue.c

···
  * @fmt:   The format for printf.
  * @...:   The args for printf.
  */
-static void cat_printf(char **buf, size_t *size, const char *fmt, ...)
+static __printf(3, 4)
+void cat_printf(char **buf, size_t *size, const char *fmt, ...)
 {
 	va_list args;
 	int i;