PM / devfreq: Use constant name of userspace governor

Based on commit aa7c352f ("PM / devfreq: Define the constant governor
name"), use constant name for userspace governor.
Signed-off-by: pierre Kuo <vichy.kuo@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/governor_userspace.c

@@ -131,7 +131,7 @@ static int devfreq_userspace_handler(struct devfreq *devfreq,
 }
 
 static struct devfreq_governor devfreq_userspace = {
-	.name = "userspace",
+	.name = DEVFREQ_GOV_USERSPACE,
 	.get_target_freq = devfreq_userspace_func,
 	.event_handler = devfreq_userspace_handler,
 };