udev: use more specific rule for creating touchscreen symlink

On the librem 5, this rule caused a symlink from /dev/input/mouse0
(which had the TOUCHSCREEN attrib set in udev... ??) to
/dev/input/touchscreen, when it should have been from something like
/dev/event*. This change causes udev to ignore mouse*, mice* etc in
/dev/input.

Tested on the librem 5.

Signed-off-by: Maarten van Gompel <proycon@anaproy.nl>

configs/udev/90-sxmo.rules

@@ -1,7 +1,7 @@
 SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="1", RUN+="/usr/bin/sxmo_statusbarupdate.sh"
 SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="0", RUN+="/usr/bin/sxmo_statusbarupdate.sh"
 
-ACTION=="add", SUBSYSTEM=="input", ENV{ID_INPUT_TOUCHSCREEN}=="1", MODE:="0666", SYMLINK+="input/touchscreen"
+ACTION=="add", SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", MODE:="0666", SYMLINK+="input/touchscreen"
 ACTION=="add", SUBSYSTEM=="input", ENV{ID_PATH}=="platform-vibrator", MODE:="0666"
 
 # taken from https://github.com/haikarainen/light/blob/master/90-backlight.rules