Use correct spelling of "U-Boot"

Correct spelling of "U-Boot" shall be used in all written text
(documentation, comments in source files etc.).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/board/freescale/mx6sxsabreauto/mx6sxsabreauto.c b/board/freescale/mx6sxsabreauto/mx6sxsabreauto.c
index c9631d2..a240982 100644
--- a/board/freescale/mx6sxsabreauto/mx6sxsabreauto.c
+++ b/board/freescale/mx6sxsabreauto/mx6sxsabreauto.c
@@ -339,7 +339,7 @@
 
 	/*
 	 * According to the board_mmc_init() the following map is done:
-	 * (U-boot device node)    (Physical Port)
+	 * (U-Boot device node)    (Physical Port)
 	 * mmc0                    USDHC3
 	 * mmc1                    USDHC4
 	 */