tests: drivers: spi_loopback: increase latency limit for nrf54h

The nrf54h20 needs a slightly increased latency limit as the latency
is around 650us at 8MHz, which is right above the current limit of
648us (CONFIG_SPI_IDEAL_TRANSFER_DURATION_SCALING=12).

Increase CONFIG_SPI_IDEAL_TRANSFER_DURATION_SCALING to 15 to match
cpuppr_xip and match the observed latency.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>
2 files changed