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.mpc83xxads b/doc/README.mpc83xxads
index d456103..7a8b706 100644
--- a/doc/README.mpc83xxads
+++ b/doc/README.mpc83xxads
@@ -80,7 +80,7 @@
 
 	tftp 10000 u-boot.bin
 
-5.1 Reflash U-boot Image using U-boot
+5.1 Reflash U-Boot Image using U-Boot
 
     tftp 10000 u-boot.bin
     protect off fe000000 fe09ffff