Vulkan broken inside Flatpak

Change introduced in !53 (merged) broke Vulkan for Flatpak apps. As @gasinvein noticed, VK_ICD_FILENAMES has wrong path for flatpak environment.

result of execution flatpak run org.freedesktop.Platform.VulkanInfo inside terminal on dGPU: https://paste.centos.org/view/b20b18a7