Respect maximum workgroup count in SpvAsmInstructionTests

The createOpAtomic group was using a hard-coded 1000000
for numElements which is later used as the workgroup count.
The minimum mandatory workgroup count is 65535, far less
than the 1000000 being used.

Affects:

dEQP-VK.spirv_assembly.instruction.compute.opatomic*

Components: Vulkan

VK-GL-CTS issue: 613

Change-Id: I523451d33dbb116e6ca2aaa00a948ec6782382b3
diff --git a/external/vulkancts/modules/vulkan/spirv_assembly/vktSpvAsmInstructionTests.cpp b/external/vulkancts/modules/vulkan/spirv_assembly/vktSpvAsmInstructionTests.cpp
index 1c264fe..ecbd17c 100644
--- a/external/vulkancts/modules/vulkan/spirv_assembly/vktSpvAsmInstructionTests.cpp
+++ b/external/vulkancts/modules/vulkan/spirv_assembly/vktSpvAsmInstructionTests.cpp
@@ -394,7 +394,7 @@
 {
 	de::MovePtr<tcu::TestCaseGroup>	group			(new tcu::TestCaseGroup(testCtx, "opatomic", "Test the OpAtomic* opcodes"));
 	de::Random						rnd				(deStringHash(group->getName()));
-	const int						numElements		= 1000000;
+	const int						numElements		= 65535;
 	vector<OpAtomicCase>			cases;
 
 	const StringTemplate			shaderTemplate	(