layers: Update pipeline multisample pnext check
layers: Update pipeline multisample pnext check

Updated validation check for
VUID-VkPipelineMultisampleStateCreateInfo-pNext-pNext
(VALIDATION_ERROR_1001c40d) to include the valid extension pNext sType
values valid for the current spec:
    VkPipelineCoverageModulationStateCreateInfoNV,
    VkPipelineCoverageToColorStateCreateInfoNV, or
    VkPipelineSampleLocationsStateCreateInfoEXT

Change-Id: Ic3e054110c2bad4b44121a67e7e61e627fa9c559

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools