usb: gadget: fix two sparse warnings

drivers/usb/gadget/u_serial.c:1291:5: sparse: symbol \
	'userial_init' was not declared. Should it be static?
drivers/usb/gadget/zero.c:66:25: sparse: symbol \
	'gzero_options' was not declared. Should it be static?
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/u_serial.c

@@ -1288,7 +1288,7 @@ void gserial_disconnect(struct gserial *gser)
 }
 EXPORT_SYMBOL_GPL(gserial_disconnect);
 
-int userial_init(void)
+static int userial_init(void)
 {
 	unsigned			i;
 	int				status;

drivers/usb/gadget/zero.c

@@ -63,7 +63,7 @@ static const char longname[] = "Gadget Zero";
 static bool loopdefault = 0;
 module_param(loopdefault, bool, S_IRUGO|S_IWUSR);
 
-struct usb_zero_options gzero_options = {
+static struct usb_zero_options gzero_options = {
 	.isoc_interval = 4,
 	.isoc_maxpacket = 1024,
 	.bulk_buflen = 4096,