usb: musb: remove extern qualifier from musb_debug.h header

This change removes confusing extern qualifier, which doesn't have any practical
sense there.
Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@nokia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_debug.h

@@ -43,8 +43,8 @@
 #define ERR(fmt, args...) yprintk(KERN_ERR, fmt, ## args)
 
 #ifdef CONFIG_DEBUG_FS
-extern int musb_init_debugfs(struct musb *musb);
-extern void musb_exit_debugfs(struct musb *musb);
+int musb_init_debugfs(struct musb *musb);
+void musb_exit_debugfs(struct musb *musb);
 #else
 static inline int musb_init_debugfs(struct musb *musb)
 {