[POWERPC] Fix irq enable/disable in smp_generic_take_timebase

Eran Ben-Avi <eranpublic@yahoo.com> pointed out that the arch/ppc version
of smp_generic_take_timebase disables interrupts on entry but exits without
restoring them.  However, both it and the arch/powerpc version have another
problem, which is that they use local_irq_disable/enable rather than
local_irq_save/restore, and they are called with interrupts disabled.

This fixes both problems; it changes a return to a break in the arch/ppc
version, and changes both versions to use local_irq_save/restore.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/smp-tbsync.c b/arch/powerpc/kernel/smp-tbsync.c
index f19e2e0..de59c6c 100644
--- a/arch/powerpc/kernel/smp-tbsync.c
+++ b/arch/powerpc/kernel/smp-tbsync.c
@@ -45,8 +45,9 @@
 {
 	int cmd;
 	u64 tb;
+	unsigned long flags;
 
-	local_irq_disable();
+	local_irq_save(flags);
 	while (!running)
 		barrier();
 	rmb();
@@ -70,7 +71,7 @@
 			set_tb(tb >> 32, tb & 0xfffffffful);
 		enter_contest(tbsync->mark, -1);
 	}
-	local_irq_enable();
+	local_irq_restore(flags);
 }
 
 static int __devinit start_contest(int cmd, long offset, int num)