[wasm] Fix OpcodeLength() calculation.

src/wasm/ast-decoder.h

Index: src/wasm/ast-decoder.h
diff --git a/src/wasm/ast-decoder.h b/src/wasm/ast-decoder.h
index c2e93311a494c4c42e449375a4538b204dfacde7..edcafa42a1a62843aebc585f9ea39d0ac308d4d4 100644
--- a/src/wasm/ast-decoder.h
+++ b/src/wasm/ast-decoder.h
@@ -46,8 +46,7 @@ struct ImmI32Operand {
   int32_t value;
   int length;
   inline ImmI32Operand(Decoder* decoder, const byte* pc) {
-    value =
-        bit_cast<int32_t>(decoder->checked_read_i32v(pc, 1, &length, "immi32"));
+    value = decoder->checked_read_i32v(pc, 1, &length, "immi32");
   }
 };
 
@@ -55,8 +54,7 @@ struct ImmI64Operand {
   int64_t value;
   int length;
   inline ImmI64Operand(Decoder* decoder, const byte* pc) {
-    value =
-        bit_cast<int64_t>(decoder->checked_read_i64v(pc, 1, &length, "immi64"));
+    value = decoder->checked_read_i64v(pc, 1, &length, "immi64");
   }
 };