[wasm] Fix to() and to_unchecked() on WasmValue

The bug was recently introduced in https://crrev.com/c/730716.

R=titzer@chromium.org

Bug: v8:6954
Change-Id: I9b77baac9fafefaab163700432ddef6e9e686901
Reviewed-on: https://chromium-review.googlesource.com/735540Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48953}

src/wasm/wasm-value.h

@@ -71,11 +71,11 @@ class WasmValue {
 #define DECLARE_CAST(name, localtype, ctype, ...) \
   template <>                                     \
   inline ctype WasmValue::to_unchecked() const {  \
-    return to_##name();                           \
+    return to_##name##_unchecked();               \
   }                                               \
   template <>                                     \
   inline ctype WasmValue::to() const {            \
-    return to_##name##_unchecked();               \
+    return to_##name();                           \
   }
 FOREACH_WASMVAL_TYPE(DECLARE_CAST)
 #undef DECLARE_CAST