PM / Hibernate: Fix ioctl SNAPSHOT_S2RAM

The SNAPSHOT_S2RAM ioctl used for implementing the feature allowing
one to suspend to RAM after creating a hibernation image is currently
broken, because it doesn't clear the "ready" flag in the struct
snapshot_data object handled by it.  As a result, the
SNAPSHOT_UNFREEZE doesn't work correctly after SNAPSHOT_S2RAM has
returned and the user space hibernate task cannot thaw the other
processes as appropriate.  Make SNAPSHOT_S2RAM clear data->ready
to fix this problem.
Tested-by: Alexandre Felipe Muller de Souza <alexandrefm@mandriva.com.br>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: stable@kernel.org

kernel/power/user.c

@@ -381,6 +381,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		 * PM_HIBERNATION_PREPARE
 		 */
 		error = suspend_devices_and_enter(PM_SUSPEND_MEM);
+		data->ready = 0;
 		break;
 
 	case SNAPSHOT_PLATFORM_SUPPORT: