setup: return proper error code from variable_set()
setup: return proper error code from variable_set()

FrozenCow/gummiboot,todorez/gummiboot-multiboot2,todorez/tummiboot,liliang365/my_gummiboot,miguelinux/gummiboot2systemd-boot,todorez/gummiboot-multiboot2,FrozenCow/gummiboot,freedesktop-unofficial-mirror/gummiboot,aaronp24/gummiboot,trilean/gummiboot,todorez/tummiboot,trilean/gummiboot,aaronp24/gummiboot,liliang365/my_gummiboot,freedesktop-unofficial-mirror/gummiboot,miguelinux/gummiboot2systemd-boot