pinctrl: cy8c95x0: Fix doc warning

One member of struct cy8c95x0_pinctrl is missing kerneldoc,
which leads to warnings.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311031342.r4To3GaD-lkp@intel.com/
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231114-cy8c95x0-doc-v1-1-31674103ad18@linaro.org