HID: fix hid->hiddev initialization in hiddev_connect()

Commit 07903407 ("HID: hiddev cleanup -- handle all error conditions
properly") by mistake removed proper initialization of hid->hiddev pointer
in hiddev_connect() in case usb_register_dev() succeeds for the hiddev node.
Put it properly back in place.

Reported-and-tested-by: Gabriel C <nix.or.die@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>