Adjust {Max,Min}Coords for {proj}offset texture tests with 3D texture targets

Adjust {Max,Min}Coords for {proj}offset texture tests with 3D texture targets

As it is now, the computed lod ends up being ~0.962, which is very close to the
threshold that separates selection of the first two mipmap levels. At least on
Intel GPUs this leads to test failures because the miplevel selected by CTS to
produce the expected result does not match the one actually selected by the
hardware.

This patch alters the coordinates used with these tests so the comuted lod
isn't too close to a mipmap level threshold.

Affects:
dEQP-VK.glsl.texture_functions.texture{proj}offset.sampler3d*

Khronos issue: #552

Change-Id: I6ec766133905d2085cd795eea8aaf0b04e830278