usb: gadget: udc: renesas_usb3: fix maxpacket size of ep0

This patch fixes an issue that maxpacket size of ep0 is incorrect
for SuperSpeed. Otherwise, CDC NCM class with SuperSpeed doesn't
work correctly on this driver because its control read data size
is more than 64 bytes.

Reported-by: Junki Kato <junki.kato.xk@renesas.com>
Fixes: 746bfe63

 ("usb: gadget: renesas_usb3: add support for Renesas USB3.0 peripheral controller")
Cc: <stable@vger.kernel.org> # v4.5+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Junki Kato <junki.kato.xk@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>