greybus: svc: fix pwrmon return value

Errno -ENOSYS is reserved for missing syscalls, replace it with ENOMSG.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/svc.c

@@ -161,7 +161,7 @@ static int gb_svc_pwrmon_sample_get(struct gb_svc *svc, u8 rail_id,
 		case GB_SVC_PWRMON_GET_SAMPLE_INVAL:
 			return -EINVAL;
 		case GB_SVC_PWRMON_GET_SAMPLE_NOSUPP:
-			return -ENOSYS;
+			return -ENOMSG;
 		default:
 			return -EIO;
 		}