hwmon: convert drivers/hwmon/* to use module_spi_driver()

This patch converts the drivers in drivers/hwmon/* to use the
module_spi_driver() macro which makes the code smaller and a bit simpler.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Sonic Zhang <sonic.zhang@analog.com>
Cc: Marc Pignat <marc.pignat@hevs.ch>
Cc: Paul Thomas <pthomas8589@gmail.com>
Cc: Eric Miao <eric.y.miao@gmail.com>
Acked-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>