anv: fix format mapping for depth/stencil formats

anv_format is supposed to have a pointer back to the associated
VkFormat, we were missed this for depth/stencil formats.

This doesn't fix anything afaict, but will be needed for future
changes.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 465de47b ("anv: associate vulkan formats with aspects")
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit 3adc32df)