hwmon: (w83781d) Add missing curly braces

Missing curly braces cause an if statement to be evaluated when it
shouldn't. It happens to be harmless, but that's still worth fixing.
Thanks to Riku Voipio for reporting.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-By: Riku Voipio <riku.voipio@movial.fi>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>