arm: support cs_regs_access() API
diff --git a/MCInst.c b/MCInst.c
index f17a942..2991c71 100644
--- a/MCInst.c
+++ b/MCInst.c
@@ -17,6 +17,7 @@
 	inst->has_imm = false;
 	inst->op1_size = 0;
 	inst->writeback = false;
+	inst->ac_idx = 0;
 }
 
 void MCInst_clear(MCInst *inst)