usb: gadget: midi: f_midi_alloc() can be static

drivers/usb/gadget/function/f_midi.c:1072:21: sparse: symbol 'f_midi_alloc' was not declared. Should it be static?
drivers/usb/gadget/legacy/gmidi.c:118:30: sparse: symbol 'fi_midi' was not declared. Should it be static?
drivers/usb/gadget/legacy/gmidi.c:119:21: sparse: symbol 'f_midi' was not declared. Should it be static?

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 1f94dad..a904403 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -1097,7 +1097,7 @@
 	usb_free_all_descriptors(f);
 }
 
-struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
+static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 {
 	struct f_midi *midi;
 	struct f_midi_opts *opts;