iio: gyro: mpu3050: fix chip ID reading

According to the datasheet, the last bit of CHIP_ID register controls
I2C bus, and the first one is unused. Handle this correctly.

Note that there are chips out there that have a value such that
the id check currently fails.

Signed-off-by: Sergey Larin <cerg2010cerg2010@mail.ru>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>