[Bug] nrf_qspi_cinstrdata_get didn't collect data from both CINSTRDAT1 and CINSTRDAT0

The function nrf_qspi_cinstrdata_get has logic bug that didn't combine data from both register

https://github.com/NordicSemiconductor/nrfx/blob/master/hal/nrf_qspi.h#L702

e.g if the length = 6, it will go into the first switch, get the first byte from CINSTRDAT1. The next switch that got data from CINSTRDAT0 will never executed since the length is 6 (out of all cases).