backend-wayland: reuse backend->formats[0] as pixman/cairo/shm pixel format
The pixel format stored in backends->format[0]
is effectively looked up via pixel_format_get_info(DRM_FORMAT_ARGB8888)
. Reuse that instead of looking up the same via pixel_format_get_info_by_pixman(PIXMAN_a8r8g8b8)
in multiple places.
There are still two instances of hard-coded CAIRO_FORMAT_ARGB32
in wayland_output_get_shm_buffer()
that currently can not be obtained from
pixel_format_info
.