pinctrl: sirf: add missing __iomem annotation

Added missing __iomem annotation in order to fix the following
sparse warnings:

drivers/pinctrl/sirf/pinctrl-sirf.c:846:14: warning: incorrect type in assignment (different address spaces)
drivers/pinctrl/sirf/pinctrl-sirf.c:846:14:    expected void *regs
drivers/pinctrl/sirf/pinctrl-sirf.c:846:14:    got void [noderef] <asn:2>*
drivers/pinctrl/sirf/pinctrl-sirf.c:869:33: warning: incorrect type in assignment (different address spaces)
drivers/pinctrl/sirf/pinctrl-sirf.c:869:33:    expected void [noderef] <asn:2>*regs
drivers/pinctrl/sirf/pinctrl-sirf.c:869:33:    got void *regs
drivers/pinctrl/sirf/pinctrl-sirf.c:909:17: warning: incorrect type in argument 1 (different address spaces)
drivers/pinctrl/sirf/pinctrl-sirf.c:909:17:    expected void volatile [noderef] <asn:2>*addr
drivers/pinctrl/sirf/pinctrl-sirf.c:909:17:    got void *regs

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>