drivers: i2s_nrfx: Add missing <hal/nrf_clock.h> inclusion

This driver uses the NRF_CLOCK_HAS_HFCLKAUDIO symbol that is defined
in <hal/nrf_clock.h>, so it should explicitly include that header,
not count on this inclusion being done by some other header, like
<zephyr/drivers/clock_control/nrf_clock_control.h>.
Extend also the build assertion that checks if the audio clock can
be used so that now it ensures that the above symbol is defined
(to prevent the driver from silently discarding the audio clock
configured as the clock source).

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