Unhardcode gpio keys device for checkstop monitor

The move to gpio-keys-polled will require evdev code to use the symlink
that the udev rule (60-persistent-input.rules) will get created.

Change-Id: I2be9dcbbf21a8bd212bc273ac488c891f07dd415
Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
diff --git a/common/recipes-phosphor/host/checkstop-monitor/obmc/gpio/checkstop b/common/recipes-phosphor/host/checkstop-monitor/obmc/gpio/checkstop
index 1259483..e6468d8 100644
--- a/common/recipes-phosphor/host/checkstop-monitor/obmc/gpio/checkstop
+++ b/common/recipes-phosphor/host/checkstop-monitor/obmc/gpio/checkstop
@@ -1,4 +1,4 @@
-PATH=/dev/input/event0
+PATH=/dev/input/by-path/platform-gpio-keys-event
 KEY=74
 POLARITY=1
 TARGET=obmc-host-crash@0.target