usb: gadget: udc: renesas_usb3: fix number of the pipes

This controller on R-Car Gen3 has 6 pipes that included PIPE 0 for
control actually. But, the datasheet has error in writing as it has
31 pipes. (However, the previous code defined 30 pipes wrongly...)

Anyway, this patch fixes it.

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>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>