adxl345: Renamed decode_samples and fixed/added checks on empty data

Signed-off-by: Dmitry Butyugin <dmbutyugin@google.com>

klippy/extras/shaper_calibrate.py

@@ -264,7 +264,10 @@ class ShaperCalibrate:
         if isinstance(raw_values, np.ndarray):
             data = raw_values
         else:
-            data = np.array(raw_values.decode_samples())
+            samples = raw_values.get_samples()
+            if not samples:
+                return None
+            data = np.array(samples)
 
         N = data.shape[0]
         T = data[-1,0] - data[0,0]