dt-bindings: rtc: ti,bq32k: take maintainership

Take maintainership of the binding as PAvel said he doesn't have the
hardware anymore.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Link: https://lore.kernel.org/r/20210620224030.1115356-1-alexandre.belloni@bootlin.com