Fix fetching geometry in dEQP-VK.renderpass test

Fix fetching geometry in dEQP-VK.renderpass test

The renderpass test uses 48 byte vertex buffer for 6x 2-element float
values. At the same time pipeline tries to fetch 4-element atributes,
so the last vertex from buffer is outside of bounds (and may be zeroed).

Affected: All dEQP-VK.renderpass* that have the render geoemtry visible
in tested attachments.

Change-Id: If58e18c4df0ea053aa0a766b2bab381a0648326f