usb: gadget: f_loopback: Fix sparse warning

Make local symbols static in order to fix the following sparse
warnings.

drivers/usb/gadget/f_loopback.c:123:34: warning: symbol 'ss_loop_source_comp_desc' was not declared. Should it be static?
drivers/usb/gadget/f_loopback.c:139:34: warning: symbol 'ss_loop_sink_comp_desc' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/f_loopback.c

@@ -120,7 +120,7 @@ static struct usb_endpoint_descriptor ss_loop_source_desc = {
 	.wMaxPacketSize =	cpu_to_le16(1024),
 };
 
-struct usb_ss_ep_comp_descriptor ss_loop_source_comp_desc = {
+static struct usb_ss_ep_comp_descriptor ss_loop_source_comp_desc = {
 	.bLength =		USB_DT_SS_EP_COMP_SIZE,
 	.bDescriptorType =	USB_DT_SS_ENDPOINT_COMP,
 	.bMaxBurst =		0,
@@ -136,7 +136,7 @@ static struct usb_endpoint_descriptor ss_loop_sink_desc = {
 	.wMaxPacketSize =	cpu_to_le16(1024),
 };
 
-struct usb_ss_ep_comp_descriptor ss_loop_sink_comp_desc = {
+static struct usb_ss_ep_comp_descriptor ss_loop_sink_comp_desc = {
 	.bLength =		USB_DT_SS_EP_COMP_SIZE,
 	.bDescriptorType =	USB_DT_SS_ENDPOINT_COMP,
 	.bMaxBurst =		0,