leds: lm36274: fix use-after-free on unbind

Several MFD child drivers register their class devices directly under
the parent device. This means you cannot use devres so that
deregistration ends up being tied to the parent device, something which
leads to use-after-free on driver unbind when the class device is
released while still being registered.

Fixes: 11e1bbc1 ("leds: lm36274: Introduce the TI LM36274 LED driver")
Cc: stable <stable@vger.kernel.org>     # 5.3
Cc: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>