hwmon: (gpd-fan) Fix return value when platform_get_resource() fails

When platform_get_resource() fails it returns NULL and not an error
pointer, accordingly change the error handling.

Fixes: 0ab88e23 ("hwmon: add GPD devices sensor driver")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Link: https://lore.kernel.org/r/20251010204359.94300-1-harshit.m.mogalapalli@oracle.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>