Driver Core: add ability for class_for_each_device to start in middle of list

This mirrors the functionality that driver_for_each_device has as well.

We add a start variable, and all callers of the function are fixed up at
the same time.

The block layer will be using this new functionality in a follow-on
patch.


Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/power/apm_power.c b/drivers/power/apm_power.c
index a489227..936bae5 100644
--- a/drivers/power/apm_power.c
+++ b/drivers/power/apm_power.c
@@ -78,7 +78,7 @@
 	main_battery = NULL;
 	bp.main = main_battery;
 
-	error = class_for_each_device(power_supply_class, &bp,
+	error = class_for_each_device(power_supply_class, NULL, &bp,
 				      __find_main_battery);
 	if (error) {
 		main_battery = bp.main;