Re-enable RE test ..._premultipliesAlpha on Graphite w/ tolerance 1

Ganesh rounds this more consistently than Graphite, but Graphite's
approach is technically more correct. See egdaniel@'s description at
b/331446496#comment5

Bug: b/331446496
Change-Id: Ib1fd7975f36ccc114cef3b0cdd60ac173df62a69
Test: librenderengine_test