42.7.5.3.3 Clock Stretching Sequence
If TWIHS_THR or TWIHS_RHR is not written/read in time, the TWIHS performs a clock stretching.
Clock stretching information is given by the SCLWS (Clock Wait State) bit.
See Clock Stretching in Read Mode and Clock Stretching in Write Mode.
Note: Clock stretching can be disabled by configuring the SCLWSDIS bit in TWIHS_SMR. In that
case, the UNRE and OVRE flags indicate an underrun (when TWIHS_THR is not filled on time)
or an overrun (when TWIHS_RHR is not read on time).