iio: gyro: ADXRS450: Add missing scale attributes

Add missing scale attributes.
Temperature data is presented as 10-bit, twos complement number.
Therefore use singed and shift accordingly.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>