[riscv64] Use s1 to save code_obj

The caller saved a4 may be clobbered by the callee function. So we substitute it with the callee saved s1 to save code_obj.

Change-Id: Iebe707cbaa62d47fdee0aa117e32e88f67dac743
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3096886Reviewed-by: Ji Qiu <qiuji@iscas.ac.cn>
Commit-Queue: Ji Qiu <qiuji@iscas.ac.cn>
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Auto-Submit: Yahan Lu <yahan@iscas.ac.cn>
Cr-Commit-Position: refs/heads/master@{#76294}

src/builtins/riscv64/builtins-riscv64.cc

@@ -3636,7 +3636,7 @@ void Generate_BaselineOrInterpreterEntry(MacroAssembler* masm,
   __ Ld(closure, MemOperand(fp, StandardFrameConstants::kFunctionOffset));
 
   // Get the Code object from the shared function info.
-  Register code_obj = a4;
+  Register code_obj = s1;
   __ LoadTaggedPointerField(
       code_obj,
       FieldMemOperand(closure, JSFunction::kSharedFunctionInfoOffset));