pinctrl: mediatek: moore: handle mtk_hw_set_value() errors in mtk_pinmux_set_mux()

pinctrl: mediatek: moore: handle mtk_hw_set_value() errors in mtk_pinmux_set_mux()

mtk_pinmux_set_mux() doesn't check the result of mtk_hw_set_value()
despite it may return a negative error code. Propagate error code
to caller functions.

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Karina Yankevich <k.yankevich@omp.ru>
Link: https://lore.kernel.org/r/20230922135926.3653428-2-k.yankevich@omp.ru
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>