vkutil: Fix compilation with older vulkan-hpp versions
vkutil: Fix compilation with older vulkan-hpp versions

In older vulkan-hpp versions the actual value of a ResultValue
cannot be accessed through the 'value' member, but can be
accessed by an implicit cast. The implicit cast has been
deprecated in header versions after 148.

vkmark/vkmark,vkmark/vkmark,vkmark/vkmark