aco: fix signed integer overflow

Fix UBSan error:
runtime error: signed integer overflow: 2147483647 + 32 cannot be represented in type 'int'

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37055>

src/amd/compiler/aco_scheduler.cpp

@@ -1207,7 +1207,7 @@ void
 schedule_block(sched_ctx& ctx, Program* program, Block* block)
 {
    ctx.last_SMEM_dep_idx = 0;
-   ctx.last_VMEM_store_idx = INT_MAX;
+   ctx.last_VMEM_store_idx = INT_MIN;
    ctx.last_SMEM_stall = INT16_MIN;
    ctx.mv.block = block;