tcg/optimize: Use fold_masks_s in fold_nand

Avoid the use of the OptContext slots.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/tcg/optimize.c b/tcg/optimize.c
index 10d1376..7fe5bd6 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -2028,14 +2028,16 @@
 
 static bool fold_nand(OptContext *ctx, TCGOp *op)
 {
+    uint64_t s_mask;
+
     if (fold_const2_commutative(ctx, op) ||
         fold_xi_to_not(ctx, op, -1)) {
         return true;
     }
 
-    ctx->s_mask = arg_info(op->args[1])->s_mask
-                & arg_info(op->args[2])->s_mask;
-    return false;
+    s_mask = arg_info(op->args[1])->s_mask
+           & arg_info(op->args[2])->s_mask;
+    return fold_masks_s(ctx, op, s_mask);
 }
 
 static bool fold_neg_no_const(OptContext *ctx, TCGOp *op)