[IA64] fix nohalt boot option

this changeset broke the "nohalt" kernel boot option.
  8df5a500

default_idle() is looking at new variable can_do_pal_halt.  However,
that variable did not get cleared upon "nohalt" boot option.  Result
is that "nohalt" option is ignored until perfmon is exercised.
Signed-off-by: NKen Chen <kenneth.w.chen@intel.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

arch/ia64/kernel/process.c

@@ -179,7 +179,7 @@ static int can_do_pal_halt = 1;
 
 static int __init nohalt_setup(char * str)
 {
-	pal_halt = 0;
+	pal_halt = can_do_pal_halt = 0;
 	return 1;
 }
 __setup("nohalt", nohalt_setup);