boards: nrf: nrfx_prs: sample.boards.nrf.nrfx_prs fails

[katgiadla]

Describe the bug
The sample samples/boards/nrf/nrfx_prs/sample.boards.nrf.nrfx_prs fails.

Observed for nrf5340dk/nrf5340/cpuapp.

To Reproduce
Steps to reproduce the behavior:

1. have nrf5340dk/nrf5340/cpuapp connected
2. go to your zephyr dir
3. call ./scripts/twister -T samples/boards/nrf/nrfx_prs -p nrf5340dk/nrf5340/cpuapp --device-testing --device-serial /dev/ttyACM1 -v --inline-logs
   See console output with error

Expected behavior
Valid console output

Impact
Not clear

Logs and console output

*** Booting Zephyr OS build v3.6.0-4041-g4efc03520966 ***
nrfx PRS example on nrf5340dk
-> press "Push button 1" to trigger a transfer
-> press "Push button 2" to switch the type of peripheral
Switched to SPIM
-- Background transfer on "spi@9000" --
Background transfer failed: -116

Environment (please complete the following information):

• OS: Ubuntu 20.04.1 LTS
• Toolchain: Zephyr SDK 0.16.5-1
• Commit SHA or Version used: v3.6.0-4041-g4efc03520966

[nordic-piks]

This happens when no loopbacks are connected (without loopbacks in place I did not noticed this issue).
However, as readme states, loopbacks are optional.