testLightNavigationBar case fail in mdpi device

The resources in mdpi device is not right, because they do not have enough specify pixels
to meet the spec of the cts testcase LightBarTests#testLightNavigationBar.

Increase the margin when checking the iconPixels color.

Bug: 110512961
Test: manual, ran the test 100 times and it passed 100 times
Test: run cts -m CtsSystemUiTestCases -t android.systemui.cts.LightBarTests#testLightNavigationBar
Change-Id: I192c2392676c71d7b664a16627bfd8922600fff4
1 file changed