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>
diff --git a/drivers/usb/gadget/zero.c b/drivers/usb/gadget/zero.c
index a331ab1..685fa68 100644
--- a/drivers/usb/gadget/zero.c
+++ b/drivers/usb/gadget/zero.c
@@ -63,7 +63,7 @@
 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,