vulkan/wsi: Convert usage of -1 to UINT32_MAX.

The integers are unsigned so they do the same but this makes it
locally more clear what happened.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6071>
2 files changed