udev: match kfd by name only — misc-class devices have no udev subsystem

The first revision guarded the kfd line with SUBSYSTEM=="misc", which never
matches (misc-class devices carry no subsystem for udev matching), so the rule
was read but never fired and /dev/kfd stayed 0660 root:render. Name-only match
applies 0666 on creation and on trigger.

Also fixes test-changed.sh to exit 0 when changed paths map to zero tests
(udev rules are mapped-but-untestable) instead of invoking bats with an empty
selection.

scripts/test-changed.sh

@@ -214,6 +214,10 @@ for path in "${CHANGED[@]}"; do
     esac
 done
 
+# Mapped-but-untestable paths (udev rules, trash moves) legitimately produce an
+# empty selection; that is a pass, not a bats usage error.
+[ "${#TESTS[@]}" -gt 0 ] || exit 0
+
 if [ "$LIST_ONLY" -eq 1 ]; then
     printf '%s\n' "${TESTS[@]}"
     exit 0