tests: drivers: nrf_lf_clock_control: Polish status messages a bit

Improve alignment in the source code and limit printed messages
(SYSTEM_CLOCK_NO_WAIT and SYSTEM_CLOCK_WAIT_FOR_* are choice options,
so it is enough to print only the enabled one).

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>