tests: boards: nrf: qdec: Fix failing drivers.sensor.qdec.pm_runtime

Test was failing because after re-enabling QDEC there is an interrupt
REPORTRDY coming after some time. Test had k_msleep(100) added to
accomodate for that but it was added after sensor_sample_fetch and
should be added before so that sample with data from REPORTRDY event
is fetched so that next read is empty as expected.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>