radv/meta: fix uninitialised stack memory usage.

radv/meta: fix uninitialised stack memory usage.

==10199== Conditional jump or move depends on uninitialised value(s)
==10199==    at 0xA107B13: radv_resume_queries (radv_meta.c:93)
==10199==    by 0xA108097: radv_meta_restore (radv_meta.c:225)
==10199==  Uninitialised value was created by a stack allocation
==10199==    at 0xA1145B2: fill_buffer_shader (radv_meta_buffer.c:171)

saved_state is never memset, so the value should be inited.

Cc: mesa-stable
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23327>