vulkan/wsi: fix s/,/;/ typo

Fixes: 59e58c34 "vulkan/wsi: Only wait on semaphores on the first swapchain"
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit e0f1f74e)