s5k3l6xx: Propagate errors correctly

Also fixes signedness issue in GPIO struct.
2 jobs for turnoff in 65 minutes and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
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passed #364615
librem5
build:aarch64

00:19:57

passed #364616
librem5:arm64
build:deb

01:05:41