touchpad-cmt: match only PID=5028 for Google's Centroiding Touchpad

Match only PID=5028 for the Centroiding touchpad to prevent affecting
other trackpads.

BUG=b/35775010
TEST=`emerge-eve chromeos-base/gestures-conf` and check that the file
     has correct content.

Change-Id: Ifc464be5e161bebe61513cf204131f8bab49677b
Reviewed-on: https://chromium-review.googlesource.com/450417
Commit-Ready: Wei-Ning Huang <wnhuang@chromium.org>
Tested-by: Wei-Ning Huang <wnhuang@chromium.org>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
diff --git a/40-touchpad-cmt.conf b/40-touchpad-cmt.conf
index e9f2315..6f68adf 100644
--- a/40-touchpad-cmt.conf
+++ b/40-touchpad-cmt.conf
@@ -45,7 +45,7 @@
 
 Section "InputClass"
     Identifier      "CMT for Google Centroiding Touchpad"
-    MatchUSBID      "18d1:*"
+    MatchUSBID      "18d1:5028"
     MatchIsTouchpad "on"
     MatchDevicePath "/dev/input/event*"