vulkan: fix potential memory leak in create_rect_list_pipeline()

vulkan: fix potential memory leak in create_rect_list_pipeline()

I was playing around with possible improvements to STACK_ARRAY(), and
one of my experiments made gcc point us that we were not freeing
'stages'.

Fixes: 514c10344e6f ("vulkan/meta: Add a concept of rect pipelines")
Reviewed-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26041>
(cherry picked from commit 17e135d3d4a4bb1d835aba6ffdf1997e23360843)