Update adafruit_74hc595.py

I'm new to Python.  Makes sense to me.

Co-authored-by: Scott Shawcroft <[email protected]>

Author: davidleedom

adafruit_74hc595.py

@@ -44,7 +44,7 @@ def __init__(self, pin_number, shift_register_74hc595):
         ShiftRegister74HC595 instance.
         """
         self._pin = pin_number
-        self._byte_pos = int(self._pin / 8)
+        self._byte_pos = self._pin // 8
         self._byte_pin = self._pin % 8
         self._shift_register = shift_register_74hc595