hwmon: (pkgtemp) align driver initialization style with coretemp

pkgtemp is derived from coretemp, so some reasonable
logics should be applied onto pkgtemp, too. Such as
the init logic here.

Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>