new helper: restore_saved_sigmask()

first fruits of ..._restore_sigmask() helpers: now we can take
boilerplate "signal didn't have a handler, clear RESTORE_SIGMASK
and restore the blocked mask from ->saved_mask" into a common
helper.  Open-coded instances switched...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/xtensa/kernel/signal.c b/arch/xtensa/kernel/signal.c
index ea7e177..8c4e751 100644
--- a/arch/xtensa/kernel/signal.c
+++ b/arch/xtensa/kernel/signal.c
@@ -532,8 +532,7 @@
 	}
 
 	/* If there's no signal to deliver, we just restore the saved mask.  */
-	if (test_and_clear_thread_flag(TIF_RESTORE_SIGMASK))
-		set_current_blocked(&current->saved_sigmask);
+	restore_saved_sigmask();
 
 	if (current->ptrace & PT_SINGLESTEP)
 		task_pt_regs(current)->icountlevel = 1;