rfkill: hide unused goto label

A cleanup introduced a harmless warning in some configurations:

net/rfkill/core.c: In function 'rfkill_init':
net/rfkill/core.c:1350:1: warning: label 'error_input' defined but not used [-Wunused-label]

This adds another #ifdef around the label to match that around the
caller.

Fixes: 6124c53e ("rfkill: Cleanup error handling in rfkill_init()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>