panfrost: Fix formats converting uninit from AFBC

panfrost: Fix formats converting uninit from AFBC

If no slices were valid (the resource is uninitialized), we were reading
a bogus PIPE_FORMAT_NONE format from the blit.dst.format. Fix this --
and guard against scope similar issues -- by hoisting the blit
assignments out of the loop so they're valid.

Fixes: 9d0ad7fd2e1 ("panfrost: Patch the gallium driver to use pan_image_layout_init()")
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10415>