Series resistor on digital signal lines
Here is a simulation of 50MHz Clock on 2cm track of 8:1 L/W ratio for the trace.

L,C is distributed track inductance and the capacitance ratio for a known 3.3V logic Vol/Iol=Zo driver impedance.

are they needed on 48MHz signal line which is cca. 2cm long?

Maybe.  Do you feel Lucky?