Despite the comment it contains, the initialization procedure for
the external memory chip on nRF5340 DK does not enable the High
Performance Mode in the chip, so communication using a frequency
higher than 8 MHz fails and the sample crashes (it works only right
after programming the chip with nrfjprog, which enables the High
Performance Mode, but the chip returns to the Low Power mode after
the board is power-cycled).
This commit fixes the initialization procedure and performs some
additional clean-up.
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
788fe5b4bf