sync: Decrease ReadStates initial capacity from 3 to 2

Author: artem-lunarg

layers/sync/sync_access_state.h

@@ -521,7 +521,7 @@ class ResourceAccessState {
 
     VkPipelineStageFlags2 last_read_stages;
     VkPipelineStageFlags2 read_execution_barriers;
-    using ReadStates = small_vector<ReadState, 3, uint32_t>;
+    using ReadStates = small_vector<ReadState, 2, uint32_t>;
     ReadStates last_reads;
 
     // TODO Input Attachment cleanup for multiple reads in a given stage