rtc: wm8350: Remove unused to_wm8350_from_rtc_dev

The to_wm8350_from_rtc_dev macro is not used by anything in the
rtc-wm8350 driver.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>