USB: ftdi_sio: remove unnecessary initialisations

Return values are being initialised to zero only to be unconditionally
assigned to a few instructions later. This may give the impression that
zero is returned on success, which is not the case.

Note also that ftdi_NDI_device_setup never reports errors.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>