udevd: fix memory leak

Re: b99028c96307e729303be8f6750418979a7488b9 shrink struct udev_event

TEST 136: test multi matches 2
device '/devices/pci0000:00/0000:00:1d.7/usb5/5-2/5-2:1.0/tty/ttyACM0' expecting node 'right'
==15011==
==15011== 7 bytes in 1 blocks are definitely lost in loss record 1 of 1
==15011==    at 0x47F9AB8: malloc (vg_replace_malloc.c:207)
==15011==    by 0x489CB5F: strdup (in /lib32/libc-2.7.so)
==15011==    by 0x8050F40: udev_rules_apply_to_event (udev-rules.c:1973)
==15011==    by 0x804A658: udev_event_execute_rules (udev-event.c:549)
==15011==    by 0x805A636: main (test-udev.c:100)
add:         ok
==15012==
==15012== 7 bytes in 1 blocks are definitely lost in loss record 1 of 1
==15012==    at 0x47F1AB8: malloc (vg_replace_malloc.c:207)
==15012==    by 0x4898B5F: strdup (in /lib32/libc-2.7.so)
==15012==    by 0x8050F40: udev_rules_apply_to_event (udev-rules.c:1973)
==15012==    by 0x804A9DF: udev_event_execute_rules (udev-event.c:658)
==15012==    by 0x805A636: main (test-udev.c:100)
remove:      ok

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>