Properly iterate over pNext in VkSamplerCreateInfo

Properly iterate over pNext in VkSamplerCreateInfo

Iterate over all pNext elements in VkSamplerCreateInfo.
Skip VkSamplerYcbcrConversionInfoKHR, retrieve
reduction mode from VkSamplerReductionModeCreateInfoEXT

VK-GL-CTS issue: 945

Components: Vulkan

Affects:
dEQP-VK.ycbcr.*
dEQP-VK.api.info.format_properties.*
dEQP-VK.pipeline.sampler.view_type.*.format.(any color format).min_reduce.*
dEQP-VK.pipeline.sampler.view_type.*.format.(any color format).mag_reduce.*
dEQP-VK.pipeline.sampler.view_type.*.format.(any depth format)

Change-Id: Iaba8678f2fa13b5545cec7f903f21aa01c5c13f3