vulkan/wsi/wayland: create swapchain using vk_zalloc()

vulkan/wsi/wayland: create swapchain using vk_zalloc()

In wsi_wl_surface_create_swapchain() we have a piece of code to init
some members of the chain to 0, in order to allow us to call
wsi_wl_swapchain_destroy() for cleanup.

Instead, we can use vk_zalloc() to allocate the chain, as it initializes
all members of the struct to zero. This help us to avoid problems when
people add new members to the struct and forget to initialize them.
Also, it makes the code look better.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12451>