Take the closest offset framebuffer.

There could be multiple, or even an exact match too.  Make sure to take
the closest one.
Ignore the high bits of the framebuffer address.

And depth buffer.  On a PSP, these bits don't affect where it renders to
even slightly.
Remove now-unnecessary MaskedEqual() compares.

Clearer this way I think.
Actually set the offset framebuffer.

Oops.
Merge pull request #6383 from unknownbrackets/gpu-minor

Check for closest render-to-tex, ignore high bits of fb addr