usb: ch9.h: usb_endpoint_maxp() uses __le16_to_cpu()

The usb/ch9.h will be installed to /usr/include/linux,
and be used from user space.
But le16_to_cpu() is only defined for kernel code.
Without this patch, user space compile will be broken.
Special thanks to Stefan Becker

Cc: stable@vger.kernel.org # 3.2
Reported-by: Stefan Becker <chemobejk@gmail.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

include/linux/usb/ch9.h

@@ -589,7 +589,7 @@ static inline int usb_endpoint_is_isoc_out(
  */
 static inline int usb_endpoint_maxp(const struct usb_endpoint_descriptor *epd)
 {
-	return le16_to_cpu(epd->wMaxPacketSize);
+	return __le16_to_cpu(epd->wMaxPacketSize);
 }
 
 /*-------------------------------------------------------------------------*/