iio: imu: inv_mpu6050: fix missing break in switch

Add missing break statement to prevent the code for case
IIO_CHAN_INFO_CALIBBIAS falling through to the default case.

Also, add a break to the default case for the switch within
case IIO_CHAN_INFO_CALIBBIAS.

Addresses-Coverity-ID: 1357377
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>