Wait after initial reset until device is ready

[Ultrawipf]

Regarding issue #27 after the initial reset the device may fail to respond immediately to the next access if there is no delay to allow the chip to start back up.
This raises an uncaught exception instead of properly waiting.

This PR retries the first access after the reset by catching the OSError after the reset until it succeeds to let the chip start back up properly.

If the device is actually not connected the initial poll will still fail properly and raise an exception.

[ladyada]

this is ok but a timeout would be preferrable

[Ultrawipf]

It could raise an exception after failing a few times to ensure it can not get stuck and wait a bit between requests.
A constant delay of 1ms instead of the waiting loop also works on my device but a dynamic waiting loop may be more reliable.

Perhaps something like this to wait after each attempt and limit the iterations:

        attempts = 10
        while attempts:
            attempts -= 1
            try:
                if not self._read_u8(_MMA8451_REG_CTRL_REG2) & 0x40 > 0:
                    # Continue if chip is ready
                    break
            # Ignore OSError. After reset the device may fail to respond
            except OSError as e:
                time.sleep(0.001)
                if not attempts:
                    raise e

[FoamyGuy]

Thank you!

This looks good to me now. Latest version added timeout after a few failed attempts at reading the register.

I don't have the breakout to test on, it's from a while ago and is out of stock.