usb: handle NULL table in usb_gadget_get_string

Allow a NULL table to be passed to usb_gadget_get_string for cases
when a string table may not be populated.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Tom Rini <trini@ti.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>

drivers/usb/gadget/usbstring.c

@@ -108,6 +108,9 @@ usb_gadget_get_string(struct usb_gadget_strings *table, int id, u8 *buf)
 	struct usb_string	*s;
 	int			len;
 
+	if (!table)
+		return -EINVAL;
+
 	/* descriptor 0 has the language id */
 	if (id == 0) {
 		buf[0] = 4;