Remove double init of spinlock in sun6i_rtc_clk_init()

Fixes: 847b8bf62eb4 ("rtc: sun6i: Expose the 32kHz oscillator")
Signed-off-by: NAlexey Klimov <alexey.klimov@arm.com>
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>