Reduce the possible range in Kconfig to the half of the possible range.
E.g. setting job to be run every 40minutes is not trivial and */40 will
not work. Instead it will run the job at minute 0, then 40, then again
at 0 (after 40min, then after 20min).

Signed-off-by: Adam Wujek <dev_public@wujek.eu>