staging:iio: Fix adis16400 channel offsets and scales

Most of the channel offsets and scales in the adis16400 are incorrect:
    * Voltage scale is off by a factor of 1000
    * Temperature scale is off by a factor of 1000
	* Temperature offset is completely wrong
	* Some of the acceleration scales are either completely wrong or have the
	  wrong unit
	* Some of the angular velocity scale are either completely wrong or have
	  the wrong unit

This patch fixes these issues. For consistency it also converts scales which are
correct to use the IIO_G_TO_M_S_2 and IIO_DEGREE_TO_RAD macro. 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>