clutter: Fix input device node path leak
==129695== 333 bytes in 18 blocks are definitely lost in loss record 33,224 of 38,707
==129695== at 0x483980B: malloc (vg_replace_malloc.c:309)
==129695== by 0x4D252D0: g_malloc (gmem.c:102)
==129695== by 0x4D3F2A0: g_strdup (gstrfuncs.c:363)
==129695== by 0x56F372F: clutter_input_device_set_property (clutter-input-device.c:218)
==129695== by 0x4C88CB6: object_set_property (gobject.c:1565)
==129695== by 0x4C88CB6: g_object_new_internal (gobject.c:1971)
==129695== by 0x4C8A848: g_object_new_valist (gobject.c:2262)
==129695== by 0x4C8AB78: g_object_new (gobject.c:1780)
==129695== by 0x592F275: meta_input_device_native_new (meta-input-device-native.c:1346)
==129695== by 0x5941165: evdev_add_device (meta-seat-native.c:1354)
==129695== by 0x5941165: process_base_event (meta-seat-native.c:1421)
==129695== by 0x5941165: process_event (meta-seat-native.c:2259)
==129695== by 0x5941165: process_events (meta-seat-native.c:2272)