score: fix bogus restarts on sigreturn()

we *really* don't want to have restart logics hit when we are returning from
sigreturn() - random replacement of %r4 with -4 just because a signal had
been noticed from timer interrupt that came when %r4 happened to contain
-514 is not nice at all.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/score/kernel/signal.c

@@ -174,6 +174,7 @@ score_rt_sigreturn(struct pt_regs *regs)
 	/* It is more difficult to avoid calling this function than to
 	   call it and ignore errors.  */
 	do_sigaltstack((stack_t __user *)&st, NULL, regs->regs[0]);
+	regs->is_syscall = 0;
 
 	__asm__ __volatile__(
 		"mv\tr0, %0\n\t"