driver core: class: Correct WARN() message in APIs class_(for_each|find)_device()

driver core: class: Correct WARN() message in APIs class_(for_each|find)_device()

For both API class_for_each_device(const struct class *class, ...) and
class_find_device(const struct class *class, ...), their WARN() messages
prompt @class was not initialized when suffer class_to_subsys(@class)
error, but the error actually means @class was not registered, so these
warning messages are not accurate.

Fix by replacing term initialized with registered within these messages.

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://lore.kernel.org/r/20241105-class_fix-v1-2-80866f9994a5@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>