thermal: imx_thermal: Do not print on error

It is not very useful to have the message below on every boot
(especially when we are using early silicon):

U-Boot 2015.10-rc2-23945-g37cf215 (Sep 08 2015 - 14:12:14 -0300)

CPU:   Freescale i.MX6UL rev1.0 792 MHz (running at 396 MHz)
CPU:   Commercial temperature grade (0C to 95C)CPU:   Thermal invalid data, fuse: 0x0
 - invalid sensor device

, so turn the error message into debug level.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

drivers/thermal/imx_thermal.c

@@ -232,7 +232,7 @@ static int imx_thermal_probe(struct udevice *dev)
 	if (is_soc_type(MXC_SOC_MX6)) {
 		/* Check for valid fuse */
 		if (fuse == 0 || fuse == ~0) {
-			printf("CPU:   Thermal invalid data, fuse: 0x%x\n",
+			debug("CPU:   Thermal invalid data, fuse: 0x%x\n",
 				fuse);
 			return -EPERM;
 		}