vulkan: don't free uninitialised memory

The modifiers array hasn't been initialised by then, much less with data
that would need freeing.
Move the label after the loop to fix this.

Fixes: c80c08e2 ("vulkan/wsi/x11: Add support for DRI3 v1.2")
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit e4fe2fd3)