hwmon: Only include of_match_table with CONFIG_OF_GPIO

The following fixes build errors on sparc. Without any DT support,
of_match_ptr is NULL and the below is a no-op. However, if just
CONFIG_OF is defined then so is of_match_ptr.

All useful parts of the gpio-fan DT support rely on CONFIG_OF_GPIO
anyway, so of_match_table should too.

Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>