rtc: sa1100: fix unbalanced clk_prepare_enable/clk_disable_unprepare

In the error path of sa1100_rtc_open(), info->clk is disabled which will
happen again in sa1100_rtc_remove() when the module is removed whereas it
is only enabled once in sa1100_rtc_init().

Fixes: 0cc0c38e ("drivers/rtc/rtc-sa1100.c: move clock enable/disable to probe/remove")
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>