csky/syscall_trace: Fixup return processing flow

The function tracehook_report_syscall_entry's return value is
__must_check attribute. We should add return processing flow in
ptrace.c and set the syscall number to -1 when failed just like
riscv's.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/include/asm/syscall.h

@@ -16,6 +16,13 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs_syscallid(regs);
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs,
+	       int sysno)
+{
+	regs_syscallid(regs) = sysno;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {

arch/csky/kernel/ptrace.c

@@ -215,7 +215,8 @@ long arch_ptrace(struct task_struct *child, long request,
 asmlinkage void syscall_trace_enter(struct pt_regs *regs)
 {
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
-		tracehook_report_syscall_entry(regs);
+		if (tracehook_report_syscall_entry(regs))
+			syscall_set_nr(current, regs, -1);
 
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
 		trace_sys_enter(regs, syscall_get_nr(current, regs));