PM / devfreq: Use constant name of userspace governor

Based on commit aa7c352f9841 ("PM / devfreq: Define the constant governor
name"), use constant name for userspace governor.

Signed-off-by: pierre Kuo <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>

drivers/devfreq/governor_userspace.c

···
 }
 
 static struct devfreq_governor devfreq_userspace = {
-	.name = "userspace",
+	.name = DEVFREQ_GOV_USERSPACE,
 	.get_target_freq = devfreq_userspace_func,
 	.event_handler = devfreq_userspace_handler,
 };