iio: imu: inv_mpu6050: fix no data on MPU6050

Some chips have a fifo overflow bit issue where the bit is always
set. The result is that every data is dropped.

Change fifo overflow management by checking fifo count against
a maximum value.

Add fifo size in chip hardware set of values.

Fixes: f5057e7b

 ("iio: imu: inv_mpu6050: better fifo overflow handling")
Cc: stable@vger.kernel.org
Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>