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/tbs/tbs2910/tbs2910.c b/board/tbs/tbs2910/tbs2910.c
index 0b509b6..7707cf5 100644
--- a/board/tbs/tbs2910/tbs2910.c
+++ b/board/tbs/tbs2910/tbs2910.c
@@ -220,7 +220,7 @@
 int board_mmc_init(bd_t *bis)
 {
 	/*
-	 * (U-boot device node)    (Physical Port)
+	 * (U-Boot device node)    (Physical Port)
 	 * mmc0                    SD2
 	 * mmc1                    SD3
 	 * mmc2                    eMMC