MINOR: pools: Cast to volatile int * instead of int *.

When using DEBUG_MEMORY_POOLS, when we want to crash, instead of using
*(int *)0 = 0, use *(volatile int *)0 = 0, or clang will just translate it
to a nop, instead of dereferencing 0.
diff --git a/include/common/memory.h b/include/common/memory.h
index 7e7d30b..9c54422 100644
--- a/include/common/memory.h
+++ b/include/common/memory.h
@@ -475,7 +475,7 @@
 #ifdef DEBUG_MEMORY_POOLS
 		/* we'll get late corruption if we refill to the wrong pool or double-free */
 		if (*POOL_LINK(pool, ptr) != (void *)pool)
-			*(int *)0 = 0;
+			*(volatile int *)0 = 0;
 #endif
 
 #ifndef DEBUG_UAF /* normal pool behaviour */