staging: slicoss: handle errors from slic_config_get

slic_config_get() can fail. Change the return type from void to
int and handle the error in slic_card_init(). So now, instead of
silently failing (and then timing out waiting for the config data),
the driver will fail loudly at request time.

Signed-off-by: David Matlack <matlackdavid@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>