rtc: sunxi: fix signedness issues

The variable year must be set as unsigned since it is used with
sunxi_rtc_data_year{.min|.max} and as parameter of is_leap_year() which
wait for unsigned int.
Only tm_year is not unsigned, but it is long.
This patch fix also the format of printing of min/max. (must use %u since
they are unsigned)

The parameter to of sunxi_rtc_setaie() must be set to uint since callers
give always uint data.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>