riscv: fix trace_sys_exit hook

Fix compilation error.
Signed-off-by: NDavid Abdurachmanov <david.abdurachmanov@gmail.com>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/ptrace.c

@@ -179,6 +179,6 @@ void do_syscall_trace_exit(struct pt_regs *regs)
 
 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
-		trace_sys_exit(regs, regs->regs[0]);
+		trace_sys_exit(regs, regs_return_value(regs));
 #endif
 }