[PATCH] Fix compiler warning in driver core for CONFIG_HOTPLUG=N

FYI, while running a build test, I found:

drivers/base/bus.c:166: warning: `driver_attr_unbind' defined but not used
drivers/base/bus.c:194: warning: `driver_attr_bind' defined but not used

Looks like these two attributes and supporting functions want to be
#ifdef HOTPLUG'd
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/bus.c

@@ -133,6 +133,8 @@ static struct kobj_type ktype_bus = {
 decl_subsys(bus, &ktype_bus, NULL);
 
 
+#ifdef CONFIG_HOTPLUG
+
 /* Manually detach a device from its associated driver. */
 static int driver_helper(struct device *dev, void *data)
 {
@@ -193,6 +195,7 @@ static ssize_t driver_bind(struct device_driver *drv,
 }
 static DRIVER_ATTR(bind, S_IWUSR, NULL, driver_bind);
 
+#endif
 
 static struct device * next_device(struct klist_iter * i)
 {