usb: gadget: udc: start_udc() can be static

Fixes the following Sparse warnings:

>> drivers/usb/gadget/udc/snps_udc_plat.c:31:6: sparse: symbol 'start_udc' was not declared. Should it be static?
>> drivers/usb/gadget/udc/snps_udc_plat.c:41:6: sparse: symbol 'stop_udc' was not declared. Should it be static?
>> drivers/usb/gadget/udc/snps_udc_plat.c:79:6: sparse: symbol 'udc_drd_work' was not declared. Should it be static?
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/snps_udc_plat.c

@@ -28,7 +28,7 @@
 /* description */
 #define UDC_MOD_DESCRIPTION     "Synopsys UDC platform driver"
 
-void start_udc(struct udc *udc)
+static void start_udc(struct udc *udc)
 {
 	if (udc->driver) {
 		dev_info(udc->dev, "Connecting...\n");
@@ -38,7 +38,7 @@ void start_udc(struct udc *udc)
 	}
 }
 
-void stop_udc(struct udc *udc)
+static void stop_udc(struct udc *udc)
 {
 	int tmp;
 	u32 reg;
@@ -76,7 +76,7 @@ void stop_udc(struct udc *udc)
 	dev_info(udc->dev, "Device disconnected\n");
 }
 
-void udc_drd_work(struct work_struct *work)
+static void udc_drd_work(struct work_struct *work)
 {
 	struct udc *udc;