acpi: fix oops in acpi_system_wakeup_device_seq_show

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 Prémont <[email protected]>
Cc: Kay Sievers <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>