imx-common: cpu: Do not print on invalid temperature

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-g37cf2152 (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: NFabio Estevam <fabio.estevam@freescale.com>

arch/arm/imx-common/cpu.c

@@ -220,9 +220,9 @@ int print_cpuinfo(void)
 		if (!ret)
 			printf(" at %dC\n", cpu_tmp);
 		else
-			puts(" - invalid sensor data\n");
+			debug(" - invalid sensor data\n");
 	} else {
-		puts(" - invalid sensor device\n");
+		debug(" - invalid sensor device\n");
 	}
 #endif