Class DATAhandle _init__() fails to pass required variable self.n_coarse_chan to DATAH

[texadactyl]

** Describe the bug
When coarse=True, self.{f_start, f_stop} are used to calculate base_header['FCNTR']. But, those 2 variables are undefined.

** Expected behavior
Pass the parameter as required.

** Setup

• Python version: 3.8
• Blimpy version: current github version