lte_sample_rates = True does not return radix-2 rates

[matth3wh]

https://github.com/srsran/srsRAN_4G/blob/ec29b0c1ff79cebcbe66caa6d6b90778261c42b8/lib/src/phy/common/phy_common.c#L353

The function srsran_symbol_sz_power2 seems to return a non-radix-2 symbol size when 75 PRB is the input. This creates an issue with using a USRP N310 at 75 PRB, as the N310 needs Radix-2 rates (https://github.com/srsran/srsRAN_4G/issues/171).

I believe simply changing the above line to return=1024 should fix the issue.