zink: dot leak dummy_buffer

Fixes: 8736ffae2ed ("zink: replace unset buffer with a dummy-buffer")

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8099>
(cherry picked from commit 07d5d911dd6c7d36fdd678f289d3babdde634406)

Conflicts:
	src/gallium/drivers/zink/zink_context.c
2 files changed