pinctrl: tb10x: Mark base as __iomem

The compile tests are complaining that this is not correctly typed.

Fixes: 1982621decaf ("pinctrl: Allow compile testing for K210, TB10X and ZYNQ")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202606150641.cbQ05ZMM-lkp@intel.com/
Signed-off-by: Linus Walleij <linusw@kernel.org>