vulkan/wsi/display: check if wsi_swapchain_init() succeeded

Fixes: da997ebe "vulkan: Add KHR_display extension using DRM [v10]"
Cc: Keith Packard <keithp@keithp.com>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit bde3102c)