acpi: fix oops in acpi_system_wakeup_device_seq_show

Commit 0794469da3f7b2093575cbdfc1108308dd3641ce: ("ACPI: struct device -
replace bus_id with dev_name(), dev_set_name()") introduced a bug by
testing 'dev_name(ldev)' instead of 'ldev->bus' for NULL when printing
out the bus information.

So if ldev->bus was NULL, we'd oops.

Reported-and-tested-by: Bruno Pr�mont <[e-mail]>
Cc: Kay Sievers <[e-mail]>
Cc: Len Brown <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/acpi/sleep/proc.c

···
 			   dev->wakeup.state.enabled ? "enabled" : "disabled");
 		if (ldev)
 			seq_printf(seq, "%s:%s",
-				   dev_name(ldev) ? ldev->bus->name : "no-bus",
+				   ldev->bus ? ldev->bus->name : "no-bus",
 				   dev_name(ldev));
 		seq_printf(seq, "\n");
 		put_device(ldev);