gpiolib: ensure that fwnode is properly set

Note that this is a RFC patch and not meant to be merged. I looked into
a problem with linux-next-20221110 on the Qualcomm SA8540P automotive
board (sc8280xp) where the UFS host controller would fail to probe due
to repeated probe deferrals when trying to get reset-gpios via
devm_gpiod_get_optional().

of_get_named_gpiod_flags() returns -EPROBE_DEFER, which is caused by
of_gpiochip_match_node_and_xlate() returning 0 since the of_xlate function
pointer is not set for the qcom,sc8280xp-tlmm pinctrl driver. The
pinctrl driver doesn't define one, so of_gpiochip_add() should
automatically setup of_gpio_simple_xlate() on it's behalf. This doesn't
happen since the fwnode member on the struct gpiochip is set to null
when of_gpiochip_add() is called. Let's work around this by ensuring
that it's set if available.

Note that this broke sometime within the last few weeks within
linux-next and I haven't bisected this. I'm posting this in the hopes
that someone may know offhand which patch(es) may have broken this.

Signed-off-by: Brian Masney <bmasney@redhat.com>
Tested-by: Marijn Suijten <marijn.suijten@somainline.org>
Tested-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Tested-by: Steev Klimaszewski <steev@kali.org> #Lenovo Thinkpad X13s
Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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