hwmon: (pmbus_core) Fix NULL pointer dereference

hwmon: (pmbus_core) Fix NULL pointer dereference

Pass i2c_client to _pmbus_is_enabled to drop the assumption
that a regulator device is passed in.

This will fix the issue of a NULL pointer dereference when called from
_pmbus_get_flags.

Fixes: df5f6b6af01c ("hwmon: (pmbus/core) Generalise pmbus get status")
Cc: stable@vger.kernel.org # v6.4
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Link: https://lore.kernel.org/r/20230725125428.3966803-2-Naresh.Solanki@9elements.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>