hwmon: (jz4740) Staticise jz4740_hwmon_driver

It is not used outside this driver so no need to make the symbol global.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>