of: add 'of_' prefix to machine_is_compatible()

machine is compatible is an OF-specific call.  It should have
the of_ prefix to protect the global namespace.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Michal Simek <monstr@monstr.eu>

drivers/macintosh/windfarm_pm91.c

@@ -711,7 +711,7 @@ static int __init wf_smu_init(void)
 {
 	int rc = -ENODEV;
 
-	if (machine_is_compatible("PowerMac9,1"))
+	if (of_machine_is_compatible("PowerMac9,1"))
 		rc = wf_init_pm();
 
 	if (rc == 0) {