staging:iio:hmc5843: Add support for spi hmc5983

This patch adds support for the hmc5983 spi interface.
This chip is almost identical to the hmc5883. The difference being added
temperature compensation, additional available sample rate (220Hz) and an SPI
interface.

Signed-off-by: Josef Gajdusek <atx@atx.name>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --cc drivers/staging/iio/magnetometer/Kconfig
Simple merge

diff --cc drivers/staging/iio/magnetometer/Makefile
Simple merge

diff --cc drivers/staging/iio/magnetometer/hmc5843_spi.c
Simple merge