arm/dts: sirf: fix the pingroup name mismatch between drivers and dts

in drivers/pinctrl/sirf, pingroup name is cko0 and cko1, but in dts, they
are cko0 and cko1_rst. this patch fixes the error in dts.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>