rtc: ingenic: Use local 'dev' variable in probe

Clean a bit the probe function by adding a local struct device *dev
variable.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200505221336.222313-2-paul@crapouillou.net


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>