kded: fix host contamination

Saw the following in kded journal:

kded6[1719]: kf.kded: /.../tmp/work/zen2-eko-linux/kded/6.5.0/recipe-sysroot-native/usr/libexec/kf6/kconf_update returned -2

Make sure KCONF_UPDATE_EXE points to the target executable and not to sysroot-native.

Signed-off-by: Marc Ferland marc.ferland@sonatest.com