usb: musb: core: remove unnecessary forward declaration

no functional changes, cleanup only.
Tested-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_core.c

@@ -508,7 +508,6 @@ void musb_hnp_stop(struct musb *musb)
 }
 
 static void musb_disable_interrupts(struct musb *musb);
-static void musb_generic_disable(struct musb *musb);
 static void musb_recover_from_babble(struct musb *musb);
 
 /*