Fix RobustnessVertexAccessInstance bounds check

Fix RobustnessVertexAccessInstance bounds check

The bounds check preformed by
VertexAccessInstance::isValueWithinVertexBufferOrZero() needs to round
the value rather than truncating it when encoding it. When
`value * 0x3FFu` is casted to a deUint32 it's possible for the result to
be truncated instead of rounded causing unintended test failures.

Affects: dEQP-VK.robustness.vertex_access.a2b10g10r10_unorm_pack32.draw.vertex_incomplete

Components: Vulkan

VK-GL-CTS issue: 1351

Change-Id: Ib034b3e29fdbbbd4670e2bbdedad07492abf5cd4