alienware-wmi: cover some scenarios where memory allocations would fail

Intel test builder caught a few instances that should test if kzalloc failed to
allocate memory as well as a scenario that platform_driver wasn't properly
initialized.

Signed-off-by: Mario Limonciello <mario_limonciello@dell.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>