Pitch Bend Step: quantization different than on TX816

[probonopd]

@Skerjanc in #884 (comment):

Pitch Bend Step:
The quantisation range is too low. E.g. set PB to 12 and PBstep to 1, you shall hear a chromatic glissando until the full octave.
But is does stop at the 11th note. This error propagates also with higher PBstep values.