PM: Clear -EAGAIN in dpm_prepare

When the last device in the dpm list is unregistered directly after its
prepare() callback returned with -EAGAIN, the return code is passed to
the calling function, resulting in a suspend failure. Prevent this by
clearing the return code after -EAGAIN.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index fae7254..58a3e57 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -762,6 +762,7 @@
 			dev->power.status = DPM_ON;
 			if (error == -EAGAIN) {
 				put_device(dev);
+				error = 0;
 				continue;
 			}
 			printk(KERN_ERR "PM: Failed to prepare device %s "