PM: sleep: Fix error handling in dpm_prepare()

Commit 2aa36604e824 ("PM: sleep: Avoid calling put_device() under
dpm_list_mtx") forgot to update the while () loop termination
condition to also break the loop if error is nonzero, which
causes the loop to become infinite if device_prepare() returns
an error for one device.

Add the missing !error check.

Fixes: 2aa36604e824 ("PM: sleep: Avoid calling put_device() under dpm_list_mtx")
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Reported-by: Thomas Hellström <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]>
Reviewed-by: Ulf Hansson <[e-mail]>
Cc: All applicable <[e-mail]>

drivers/base/power/main.c

···
 	device_block_probing();
 
 	mutex_lock(&dpm_list_mtx);
-	while (!list_empty(&dpm_list)) {
+	while (!list_empty(&dpm_list) && !error) {
 		struct device *dev = to_device(dpm_list.next);
 
 		get_device(dev);