iio:gyro: bug on L3GD20H gyroscope support

The driver was not able to manage the sensor: during probe function
and wai check, the driver stops and writes: "device name and WhoAmI mismatch."
The correct value of L3GD20H wai is 0xd7 instead of 0xd4.
Dropped support for the sensor.

Signed-off-by: Denis Ciocca <denis.ciocca@st.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>