staging:iio: Fix adis16260 channel offsets and scales

Most of the channel offsets and scales in the adis16260 are incorrect:
	* Temperature scale is off by a factor of 1000
	* Voltage scale is off by a factor of 1000
	* Temperature offset is completely wrong

This patch fixes these issues. Also use the IIO_DEGREE_TO_RAD for the angle
velocity since this makes it much easier to compare it to the value given in the
datasheet.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>