fbd-ledctrl: fix matching of trigger in list of triggers

If the trigger is the last thing in sysfs_path/LED_TRIGGER_ATTR, then
the new-line at the end of the output causes g_strv_contains to fail to
find the trigger in the list. This strips the new-line before splitting
the output into a list for searching.

You can see the problem this patch fixes with the librem 5, by:

$ rmmod ledtrig-timer     # or whatever is listed at the end, so 'pattern' is the last thing
$ cat /sys/devices/platform/pwmleds/leds/blue:status/trigger
[none] kbd-scrolllock ... pattern
$ fbd-ledctrl -p /sys/devices/platform/pwmleds/leds/blue:status -t pattern
Failed to set perms of /sys/devices/platform/pwmleds/leds/blue:status/pattern to 101: No such file or directory
$ modprobe ledtrig-timer
$ cat /sys/devices/platform/pwmleds/leds/blue:status/trigger
[none] kbd-scrolllock ... pattern timer
$ fbd-ledctrl -p /sys/devices/platform/pwmleds/leds/blue:status -t pattern
<success>
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