pinctrl: loongson2: Fix some const correctness

The kernel robot using sparse is complaining like this:

drivers/pinctrl/pinctrl-loongson2.c:212:21: sparse:
sparse: incorrect type in argument 1 (different address spaces) @@
expected void const volatile [noderef] __iomem *addr @@
got void *[noderef] __iomem reg @@
(...)

I think the problem is simply that the register base is defined
as void * __iomem instead of void __iomem * and this is because
of the way const correctness works with pointer infix order.

Fix it up. I think.

Reported-by: kernel test robot <lkp@intel.com>
Cc: zhanghongchen <zhanghongchen@loongson.cn>
Cc: Yinbo Zhu <zhuyinbo@loongson.cn>
Fixes: f73f88acbc18 ("pinctrl: pinctrl-loongson2: add pinctrl driver support")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

pinctrl: pinctrl-loongson2: add pinctrl driver support

The Loongson-2 SoC has a few pins that can be used as GPIOs or take
multiple other functions. Add a driver for the pinmuxing.

There is currently no support for GPIO pin pull-up and pull-down.

Signed-off-by: zhanghongchen <zhanghongchen@loongson.cn>
Co-developed-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Link: https://lore.kernel.org/r/20221114024942.8111-1-zhuyinbo@loongson.cn
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>