zink: fix up swapchain depth buffer geometry during fb update

due to desync between the frontend and the driver, the size that the
depth buffer was created with may not match the size of the swapchain if
the window is being resized very quickly, so just go ahead and clobber
the existing depth buffer with a series of very illegal internal object
replacements to make everything match up

do not try at home.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <!16151>
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