dts: arm: st: u5: fix wkup-pin@8 referencing non-existent port gpiof

With commit d280d892 the gpiof port got moved from file stm32u5.dtsi to
file stm32u5_extra.dtsi. stm32u5_extra.dtsi is not included for
STM32U535/545. In same file stm32u5.dtsi still node wkup-pin@8 references
non-existent port gpiof.

Fixes #93445

Signed-off-by: Andreas Schmidt <andreas.schmidt@dormakaba.com>