Fixed issue 31 PCA9685 configured to take i2c commands from all addresses

Issue description:
I'm combining my PCA9685 with HT16K33 8x8 matrix.
As soon as I send a command to the HT1633 the PCA stops responding and all my connected servos go limp.

The solution for this issue was identified here: rwaldron/johnny-five#1591 (comment)

It appears the issue was fixed in the arduino library but not corrected in circuit python (see adafruit/Adafruit-PWM-Servo-Driver-Library@9f8e1dd#diff-5d1e3a5213c0ef6dedb2baf5cc323727L106-R110)

I confirmed the fix below works for me:
Change line 163 of adafruit_pca9685 in frequency(self, freq) from
self.mode1_reg = old_mode | 0xa1 # Mode 1, autoincrement on
to
self.mode1_reg = old_mode | 0xa0 # Mode 1, autoincrement on, fix to stop pca9685 from accepting commands at all addresses

I will submit a pull request with this change.

Author: ScottMonaghan

adafruit_pca9685.py

@@ -160,7 +160,7 @@ def frequency(self, freq):
         self.prescale_reg = prescale  # Prescale
         self.mode1_reg = old_mode  # Mode 1
         time.sleep(0.005)
-        self.mode1_reg = old_mode | 0xA1  # Mode 1, autoincrement on
+        self.mode1_reg = old_mode | 0xa0 # Mode 1, autoincrement on, fix to stop pca9685 from accepting commands at all addresses
 
     def __enter__(self):
         return self
@@ -170,4 +170,4 @@ def __exit__(self, exception_type, exception_value, traceback):
 
     def deinit(self):
         """Stop using the pca9685."""
-        self.reset()
+        self.reset()