Wire up sample mask correctly

Bug: b/118386749
Change-Id: I4d6150907a0afea8eeff28334dae1e4af6309075
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/26309
Tested-by: Chris Forbes <chrisforbes@google.com>
Presubmit-Ready: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Vulkan/VkPipeline.cpp

diff --git a/src/Vulkan/VkPipeline.cpp b/src/Vulkan/VkPipeline.cpp
index c6b65ed..e619a03 100644
--- a/src/Vulkan/VkPipeline.cpp
+++ b/src/Vulkan/VkPipeline.cpp
@@ -350,10 +350,11 @@
 			UNIMPLEMENTED("Unsupported sample count");
 		}
 
+		if (multisampleState->pSampleMask)
+			context.sampleMask = multisampleState->pSampleMask[0];
+
 		if((multisampleState->flags != 0) ||
 			(multisampleState->sampleShadingEnable != 0) ||
-			!((multisampleState->pSampleMask == nullptr) ||
-			(*(multisampleState->pSampleMask) == 0xFFFFFFFFu)) ||
 				(multisampleState->alphaToCoverageEnable != 0) ||
 			(multisampleState->alphaToOneEnable != 0))
 		{