media: usb: siano: Fix false-positive "uninitialized variable" warning

GCC complains about an apparently uninitialized variable recently
added to smsusb_init_device().  It's a false positive, but to silence
the warning this patch adds a trivial initialization.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: kbuild test robot <lkp@intel.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>