pinctrl: stm32: fix the reported number of GPIO lines per bank

pinctrl: stm32: fix the reported number of GPIO lines per bank

Each GPIO bank supports a variable number of lines which is usually 16, but
is less in some cases : this is specified by the last argument of the
"gpio-ranges" bank node property.
Report to the framework, the actual number of lines, so the libgpiod
gpioinfo command lists the actually existing GPIO lines.

Fixes: 1dc9d289154b ("pinctrl: stm32: add possibility to use gpio-ranges to declare bank range")
Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Link: https://lore.kernel.org/r/20210617144629.2557693-1-fabien.dessenne@foss.st.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>