platform/x86: sony-laptop: Fix error handling in sony_nc_setup_rfkill()

Source code review for a specific software refactoring showed the need
for another correction because the error code "-1" was returned so far
if a call of the function "sony_call_snc_handle" failed here.
Thus assign the return value from these two function calls also to
the variable "err" and provide it in case of a failure.

Fixes: d6f15ed8 ("sony-laptop: use soft rfkill status stored in hw")
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lkml.org/lkml/2017/10/31/463
Link: https://lkml.kernel.org/r/<CAHp75VcMkXCioCzmLE0+BTmkqc5RSOx9yPO0ectVHMrMvewgwg@mail.gmail.com

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