USB Elan FTDI: check for workqueue creation

Avoid NULL pointer usage if workqueue creation failed.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>