Correct opatomic_storage_buffer_volatile tests

Correct opatomic_storage_buffer_volatile tests

numWorkGroups used in volatile atomics tests was higher than minimal
value that should be supported by implementation. This change reduces
it to minimal value of maxComputeWorkGroupCount. Note that in this
case we can't query limit properties as we don't have access to
Context at shader construction level.

Components: Vulkan

VK-GL-CTS public issue: 203

Affects:
dEQP-VK.spirv_assembly.instruction.compute.opatomic_storage_buffer_volatile.*

Change-Id: Ibf91e5629431525a195a2221ee65371ed1ba8809