ext4_bcache: remove buffer from LRU tree when it will be dropped.

lwext4/ext4_bcache.c

@@ -163,10 +163,10 @@ void ext4_bcache_drop_buf(struct ext4_bcache *bc, struct ext4_buf *buf)
 		ext4_dbg(DEBUG_BCACHE, DBG_WARN "Buffer is still referenced. "
 				"lba: %" PRIu64 ", refctr: %" PRIu32 "\n",
 				buf->lba, buf->refctr);
-	}
+	} else
+		RB_REMOVE(ext4_buf_lru, &bc->lru_root, buf);
 
 	RB_REMOVE(ext4_buf_lba, &bc->lba_root, buf);
-	RB_REMOVE(ext4_buf_lru, &bc->lru_root, buf);
 
 	/*Forcibly drop dirty buffer.*/
 	if (ext4_bcache_test_flag(buf, BC_DIRTY))