staging:iio: Fix adis16240 channel offsets and scales

Most of the channel offsets and scales in the adis16240 are incorrect:
    * Temperature scale is of by a factor of 1000
    * Voltage scale is of by a factor of 1000
    * Temperature offset is completely wrong
	* Peak scale is completely wrong

This patch fixes these issues. Also use the IIO_G_TO_M_S_2 macro for the
acceleration scale 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>