A test was checking that if we have less than 4 channels, and no
GL_EXT_texture_rg, we would expect an invalid operation.

Now that we don't expose GL_EXT_texture_rg on DX9, this is firing, and
I believe incorrectly.  I've changed the condition to test for less than
3 channals, since RGB -> RGB should work fine without texture_rg
support.

Change-Id: I9955b143c37df9762e0ef45c987581fab2bbcef0
Reviewed-on: https://chromium-review.googlesource.com/255933Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>