PM: Use pm_wakeup_pending() in __device_suspend()

Before starting to suspend a device in __device_suspend() check if
there's a request to abort the power transition and return -EBUSY
in that case.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 8a52583..fb4ca28 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -877,6 +877,11 @@
 	if (async_error)
 		goto End;
 
+	if (pm_wakeup_pending()) {
+		async_error = -EBUSY;
+		goto End;
+	}
+
 	if (dev->class) {
 		if (dev->class->pm) {
 			pm_dev_dbg(dev, state, "class ");