The initialization of pin_reg is missing, causing the following build
warning:

drivers/pinctrl/freescale/pinctrl-imx8ulp.c:228:35: warning: 'pin_reg' is used uninitialized in this function [-Wuninitialized]

Initialize pin_reg the same way as it is done on vf610 and imx7ulp
to fix the problem.

Fixes: 16b343e8 ("pinctrl: imx8ulp: Add pinctrl driver support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210723203242.88845-1-festevam@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>