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/doc/README.imx6 b/doc/README.imx6
index 7c9a4ac..1823fb2 100644
--- a/doc/README.imx6
+++ b/doc/README.imx6
@@ -37,7 +37,7 @@
 bank = 4
 word = 2
 
-And the U-boot command would be:
+And the U-Boot command would be:
 
 => fuse read 4 2
 Reading bank 4:
@@ -58,7 +58,7 @@
 bank = 4
 word = 3
 
-And the U-boot command would be:
+And the U-Boot command would be:
 
 => fuse read 4 3
 Reading bank 4: