rtc: class: fix double free in rtc_register_device() error path

Commit 59cca865 ("drivers/rtc/class.c: fix device_register() error
handling") correctly noted that naked kfree() should not be used after
failed device_register() call, however, while it added the needed
put_device() it forgot to remove the original kfree() causing double-free.

Cc: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>