clk: sunxi-ng: sun6i-rtc: include clk/sunxi-ng.h

clk: sunxi-ng: sun6i-rtc: include clk/sunxi-ng.h

This solves:
>> drivers/clk/sunxi-ng/ccu-sun6i-rtc.c:334:5: warning: no previous prototype for 'sun6i_rtc_ccu_probe' [-Wmissing-prototypes]
     334 | int sun6i_rtc_ccu_probe(struct device *dev, void __iomem *reg)
         |     ^~~~~~~~~~~~~~~~~~~

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220320210905.6606-1-alexandre.belloni@bootlin.com