usb: renesas_usbhs: Don't check CSSTS bit if peripheral mode

Since Some SoCs (e.g. R-Car Gen2) don't have the CSSTS bit in the
pipectrl registers ({DCP,PIPEn}CTR) because such SoCs have peripheral
mode only. So, this driver should not check the CSSTS bit if peripheral
mode is running.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>