libgui_test: increase the tolerance for a YUV test

This change increases the pixel difference tolerance of the
SurfaceTextureGLTest.TexturingFromCpuFilledYV12BufferNpot test from 2 to 3.

Bug: 8349135
Change-Id: I82e361a689335f49065cacd8a3fc145d67b125f1
1 file changed