alpha: get rid of switch_stack argument of do_work_pending()

... and now the asm glue side of that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/alpha/kernel/signal.c b/arch/alpha/kernel/signal.c
index d0b3507..32575f8 100644
--- a/arch/alpha/kernel/signal.c
+++ b/arch/alpha/kernel/signal.c
@@ -568,8 +568,7 @@
 }
 
 void
-do_work_pending(struct pt_regs *regs, struct switch_stack *unused,
-		 unsigned long thread_flags,
+do_work_pending(struct pt_regs *regs, unsigned long thread_flags,
 		 unsigned long r0, unsigned long r19)
 {
 	do {