pinctrl: sophgo: cv18xx: fix missed __iomem type identifier

pinctrl: sophgo: cv18xx: fix missed __iomem type identifier

As the variable reg in "cv1800_pctrl_dbg_show" misses a "__iomem"
type identifier, a warning will be issued by the compiler. Add
this identifier to avoid this warning.

Fixes: a29d8e93e710 ("pinctrl: sophgo: add support for CV1800B SoC")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408271555.kpOmi9I8-lkp@intel.com/
Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Link: https://lore.kernel.org/IA1PR20MB495329EBE498DFFDAA1EC457BB972@IA1PR20MB4953.namprd20.prod.outlook.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>