drivers: clock_control: smartbond: Fix rc32k calibration

If RC32K oscillator was on during startup, calibration
work was never going to actually calibrate this oscillator.
It happen because lpc_clock_state.rc32k_started was only set when
oscillator was turned on after if was turned off.

Now lpc_clock_state.rc32k_started is also set when rc32k is already
started (possible during boot).

Signed-off-by: Jerzy Kasenberg <jerzy.kasenberg@codecoup.pl>