usb: gadget: renesas_usbhs: cleanup usbhsh_endpoint_xxx()

this patch cleanup
 - make sure static function
 - remove unneeded label
 - useless local variable were removed

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>