dts/imx: rename uart labels to consistent with hw spec

UART1/UART2/... is more readable than UART0/UART1/... .
Remove redundant UART comments.

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/boot/dts/imx6q-sabreauto.dts b/arch/arm/boot/dts/imx6q-sabreauto.dts
index cd11ab0..eef6d64 100644
--- a/arch/arm/boot/dts/imx6q-sabreauto.dts
+++ b/arch/arm/boot/dts/imx6q-sabreauto.dts
@@ -44,7 +44,7 @@
 				status = "okay";
 			};
 
-			uart3: uart@021f0000 { /* UART4 */
+			uart4: uart@021f0000 {
 				status = "okay";
 			};
 		};