Fix Block decorations in 8-bit storage tests

Fix Block decorations in 8-bit storage tests

The Vulkan environment spec allows two types of SSBO declarations:

 - Storage class of Uniform with the BufferBlock decoration
 - Storage class of StorageBuffer with the Block decoration

All of the 8-bit storage tests, as far as I can see, have chosen to use
the StorageBuffer storage class.  However, most of the SSBO declarations
are missing the Block decoration entirely.  A few mistakenly have a
BufferBlock decoration.

Affects:

dEQP-VK.spirv_assembly.instruction.graphics.8bit_storage.*

Components: Vulkan

VK-GL-CTS issue: 1519
Change-Id: Id78cae9c1813cd04daa894779aa3fbec57240eb8