usb: musb: gadget: fix to_musb_ep() to not return NULL

UDC core ensures the usb_ep parameter passed in is not NULL, so
checking if (ep != NULL) is pointless.

Convert to_musb_ep() to a simple macro to not directly return NULL to
avoid warnings from code static analysis tools.
Signed-off-by: NBin Liu <b-liu@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/musb/musb_gadget.h

@@ -96,10 +96,7 @@ struct musb_ep {
 	u8				hb_mult;
 };
 
-static inline struct musb_ep *to_musb_ep(struct usb_ep *ep)
-{
-	return ep ? container_of(ep, struct musb_ep, end_point) : NULL;
-}
+#define to_musb_ep(ep)	container_of((ep), struct musb_ep, end_point)
 
 static inline struct musb_request *next_request(struct musb_ep *ep)
 {