iio:bma180: Expose temperature channel

8-bit signed; 0 LSB @ 24 °C, 0.5 °C per LSB

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Cc: Oleksandr Kravchenko <o.v.kravchenko@globallogic.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>