gpio: nomadik: make clock optional

Not all platforms using this platform driver expose a clock for this
GPIO controller. Turn devm_clk_get() into devm_clk_get_optional() to
avoid failing when no clocks are provided.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://lore.kernel.org/r/20240228-mbly-gpio-v2-20-3ba757474006@bootlin.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>