staging: iio: hmc5843: Set iio name property in sysfs

Without this change file name for hmc5843 is empty in
/sys/bus/iio/devices/iio\:device*/name

With this change name is reported correctly:
cat /sys/bus/iio/devices/iio\:device*/name
hmc5843

Signed-off-by: Marek Belisko <marek@goldelico.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>