This is a follow-up to commit 7a2ce2882a.
Inclusion of <hal/nrf_clock.h> should not be done based on the NRF_CLOCK
symbol being defined, because it depends on the order in which headers
are included - that symbol gets defined when <nrfx.h> gets included and
this is not necessarily always happening earlier. Instead of adding
inclusion of <nrfx.h> here, move inclusion of <hal/nrf_clock.h> under
`#if defined(CONFIG_CLOCK_CONTROL_NRF)` where it is actually needed.
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>