anv: avoid warning when switching in VkStructureType

anv: avoid warning when switching in VkStructureType

When one of the cases is not part of the enum, the compilar complains:

../../src/intel/vulkan/anv_formats.c: In function ‘anv_GetPhysicalDeviceFormatProperties2’:
../../src/intel/vulkan/anv_formats.c:728:7: warning: case value ‘1000001004’ not in enumerated type ‘VkStructureType’ {aka ‘enum VkStructureType’} [-Wswitch]
       case VK_STRUCTURE_TYPE_WSI_FORMAT_MODIFIER_PROPERTIES_LIST_MESA:
       ^~~~

Given the switch has an "default:" case, we don't lose anything by
switching on the unsigned value to avoid the warning.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>