w1: disable irqs in critical section

Interrupting w1_delay() in w1_read_bit() results in missing the low level
on the w1 line and receiving "1" instead of "0".

Add local_irq_save()/local_irq_restore() around the critical section

Signed-off-by: Jan Weitzel <j.weitzel@phytec.de>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/w1/w1_io.c

@@ -158,13 +158,18 @@ EXPORT_SYMBOL_GPL(w1_write_8);
 static u8 w1_read_bit(struct w1_master *dev)
 {
 	int result;
+	unsigned long flags;
 
+	/* sample timing is critical here */
+	local_irq_save(flags);
 	dev->bus_master->write_bit(dev->bus_master->data, 0);
 	w1_delay(6);
 	dev->bus_master->write_bit(dev->bus_master->data, 1);
 	w1_delay(9);
 
 	result = dev->bus_master->read_bit(dev->bus_master->data);
+	local_irq_restore(flags);
+
 	w1_delay(55);
 
 	return result & 0x1;