analyzer-driver: use default depth from config

The configuration already knows what the default depth is, so just use
the default depth from there.

Also set the default offset to 0, since that is frequently a good default.

Signed-off-by: Sean Cross <sean@xobs.io>

litescope/software/driver/analyzer.py

@@ -91,7 +91,9 @@ class LiteScopeAnalyzerDriver:
     def configure_subsampler(self, value):
         self.subsampler_value.write(value-1)
 
-    def run(self, offset, length):
+    def run(self, offset = 0, length = None):
+        if length is None:
+            length = self.depth
         assert offset < self.depth
         assert length <= self.depth
         if self.debug: