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/lib/zlib/inffast.c b/lib/zlib/inffast.c
index 0700e04..e3c7f3b 100644
--- a/lib/zlib/inffast.c
+++ b/lib/zlib/inffast.c
@@ -3,7 +3,7 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
-/* U-boot: we already included these
+/* U-Boot: we already included these
 #include "zutil.h"
 #include "inftrees.h"
 #include "inflate.h"