Fix the bilinear filtering on the Skia blur

We had bilinear sampling turned off when drawing the 0.25x sized texture
back to the framebuffer, so with blur enabled every 4x4 group of pixels
behind the blur was showing exactly the same. Ouch.

Test: Manual (see images in bug) - need to add a screenshot test
Fix: 174949985
Change-Id: I2233bc9d1b7c23ee37fba5ed5044b96c4ba4ec02