hwmon: (w83627ehf) Fix broken driver init

Commit 2265cef2 (hwmon: (w83627ehf) Properly report PECI and AMD-SI
sensor types) results in kernel panic if data->temp_label was not
initialized.
The problem was found with chip W83627DHG-P.

Add check if data->temp->label was set before use.

Based on incomplete patch by Alexander Beregalov.

Reported-by: Alexander Beregalov <a.beregalov@gmail.com>
Tested-by: Alexander Beregalov <a.beregalov@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>