Instrumentation: Update to store sample rate in MeasurementCSV file.

This commit updates existing instruments to store their sample rates
when creating the respective MeasurementCsv files.
diff --git a/devlib/instrument/daq.py b/devlib/instrument/daq.py
index 58d2f3e..75e854d 100644
--- a/devlib/instrument/daq.py
+++ b/devlib/instrument/daq.py
@@ -126,7 +126,7 @@
                     writer.writerow(row)
                     raw_row = _read_next_rows()
 
-            return MeasurementsCsv(outfile, self.active_channels)
+            return MeasurementsCsv(outfile, self.active_channels, self.sample_rate_hz)
         finally:
             for fh in file_handles:
                 fh.close()