ASoC: imx-ssi: Say if we fail to register a second AC'97 bus

Saves anyone wondering what happened if they run into this error.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/fsl/imx-ssi.c

@@ -560,6 +560,7 @@ static int imx_ssi_probe(struct platform_device *pdev)
 
 	if (ssi->flags & IMX_SSI_USE_AC97) {
 		if (ac97_ssi) {
+			dev_err(&pdev->dev, "AC'97 SSI already registered\n");
 			ret = -EBUSY;
 			goto failed_register;
 		}