rtc: isl12022: use dev_set_drvdata() instead of i2c_set_clientdata()

As another preparation for removing direct references to the
i2c_client in the helper functions, stash a pointer to the private
data via dev_set_drvdata() instead of i2c_set_clientdata().

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20220921114624.3250848-7-linux@rasmusvillemoes.dk


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