fix: remove bogus sampling rate check

[wucke13]

The plutosdr only accepts a value of datatype integer as sampling rate. For this, there already is a conversion logic, to convert float data type sampling rate values to integer data type. However, the conversion logic is flawed, as it only triggers for values of float data type if the floating point number has decimals (digits behind the dot). Therefore, values of floating point data type like 10 or 25000 are not converted to an integer data type, resulting in failure to initialize the plutosdr.

This patch removes the bogus check, always converting to integer type.

This is a fix to https://github.com/igorauad/gr-dvbs2rx/issues/38