Fix wrong constant for R8 GL upload

GL_RED + GL_UNSIGNED_BYTE is the pairing for R8 for
glTex(Sub)Image2D, not GL_R8

Test: adb shell setprop debug.hwui.renderer skiagl && atest android.graphics.cts.GainmapTest
Fixes: 319734219
Change-Id: I73874e22f8958e4aaa52963546674ec9946f8013
1 file changed