clk: sunxi-ng: sun6i-rtc: Mark rtc-32k as critical

Because some newer hardware variants have multiple possible parents for
the RTC's timekeeping clock, this driver models it as a "rtc-32k" clock.
However, it does not add any consumer for this clock. This causes the
common clock framework to disable it, preventing RTC time access.

Since the RTC's timekeeping clock should always be enabled, regardless
of which drivers are loaded, let's mark this clock as critical instead
of adding a consumer in the RTC driver.

Fixes: d91612d7

 ("clk: sunxi-ng: Add support for the sun6i RTC clocks")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220411050100.40964-1-samuel@sholland.org