r600: fix refcnt imbalance related to evergreen_set_shader_images()

r600: fix refcnt imbalance related to evergreen_set_shader_images()

Indeed, the reference was overwritten.

For instance, this issue is triggered with:
"piglit/bin/shader_runner tests/spec/arb_shader_image_load_store/execution/write-to-rendered-image.shader_test -auto -fbo"
while setting GALLIUM_REFCNT_LOG=refcnt.log.

Fixes: a6b379284365 ("r600: add core pieces of image support.")
Signed-off-by: Patrick Lerda <patrick9876@free.fr>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22394>