hp-wmi: add return value checking for input_allocate_device()

Add error checking and return -ENOMEM if input_allocate_device() fail.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Cc: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>