Looks like trigger_udev_sysname variable stays valid only because
udev_device_new_from_syspath() return value is leaked in trigger_init().

Take a copy of udev_device_get_sysname() return value instead on relying on
borrowed string pointer staying valid.

Remove all mid-function returns, release unneeded resources on success, and
all acquired resources in case of failure.

Having a boolean function return false on success / true on failure is
a bit confusing, so rectify that while at it.
Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>