Use overflow flag in example

Would have liked to implement ADC overflow detection but no flag appears to exist for it

Author: WizardTim

examples/ina219_simpletest.py

@@ -42,4 +42,9 @@
     print("Power Register : {:6.3f}   W".format(power))
     print("")
 
+    # Check internal calculations haven't overflowed (doesn't detect ADC overflows)
+    if ina219.overflow:
+        print("Internal Math Overflow Detected!")
+        print("")
+
     time.sleep(2)