usb: renesas_usbhs: protect the CFIFOSEL setting in usbhsg_ep_enable()

This patch fixes an issue that the CFIFOSEL register value is possible
to be changed by usbhsg_ep_enable() wrongly. And then, a data transfer
using CFIFO may not work correctly.

For example:
 # modprobe g_multi file=usb-storage.bin
 # ifconfig usb0 192.168.1.1 up
 (During the USB host is sending file to the mass storage)
 # ifconfig usb0 down

In this case, since the u_ether.c may call usb_ep_enable() in
eth_stop(), if the renesas_usbhs driver is also using CFIFO for
mass storage, the mass storage may not work correctly.

So, this patch adds usbhs_lock() and usbhs_unlock() calling in
usbhsg_ep_enable() to protect CFIFOSEL register. This is because:
 - CFIFOSEL.CURPIPE = 0 is also needed for the pipe configuration
 - The CFIFOSEL (fifo->sel) is already protected by usbhs_lock()

Fixes: 97664a20 ("usb: renesas_usbhs: shrink spin lock area")
Cc: <stable@vger.kernel.org> # v3.1+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>