platform/x86: sony-laptop: Drop variable assignment in sony_nc_setup_rfkill()

The local variable "err" will eventually be set to an appropriate value
a bit later. Thus omit the explicit initialisation at the beginning.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>