iris: quiet down static analyzers

Signed-off-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6067>

src/gallium/drivers/iris/iris_bufmgr.c

@@ -333,6 +333,8 @@ vma_free(struct iris_bufmgr *bufmgr,
    if (memzone == IRIS_MEMZONE_BINDER)
       return;
 
+   assert(memzone < ARRAY_SIZE(bufmgr->vma_allocator));
+
    util_vma_heap_free(&bufmgr->vma_allocator[memzone], address, size);
 }