[wasm] Exclude receiver from param count in WasmResume builtin

R=jkummerow@chromium.org
CC=fgm@chromium.org

Change-Id: I57c1860ef35919cdc7752e1dcc1beccfb4282b90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3555770Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79777}

src/builtins/x64/builtins-x64.cc

@@ -4035,6 +4035,7 @@ void Builtins::Generate_WasmResume(MacroAssembler* masm) {
   __ EnterFrame(StackFrame::STACK_SWITCH);
 
   Register param_count = rax;
+  __ decq(param_count);                    // Exclude receiver.
   Register closure = kJSFunctionRegister;  // rdi
 
   // These slots are not used in this builtin. But when we return from the