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/uImage.FIT/kernel_fdt.its b/doc/uImage.FIT/kernel_fdt.its
index 7e940d2..7c52148 100644
--- a/doc/uImage.FIT/kernel_fdt.its
+++ b/doc/uImage.FIT/kernel_fdt.its
@@ -1,5 +1,5 @@
 /*
- * Simple U-boot uImage source file containing a single kernel and FDT blob
+ * Simple U-Boot uImage source file containing a single kernel and FDT blob
  */
 
 /dts-v1/;