HID: uhid: fix leak for 64/32 UHID_CREATE

UHID allows short writes so user-space can omit unused fields. We
automatically set them to 0 in the kernel. However, the 64/32 bit
compat-handler didn't do that in the UHID_CREATE fallback. This will
reveal random kernel heap data (of random size, even) to user-space.

Fixes: befde022

 ('HID: uhid: make creating devices work on 64/32 systems')

Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>