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.video b/doc/README.video
index 62ac17b..e7ae98a 100644
--- a/doc/README.video
+++ b/doc/README.video
@@ -32,13 +32,13 @@
 Example: video-mode=fslfb:1280x1024-32@60,monitor=dvi
 
 
-U-boot sunxi video controller driver
+U-Boot sunxi video controller driver
 ====================================
 
-U-boot supports hdmi and lcd output on Allwinner sunxi SoCs, lcd output
+U-Boot supports hdmi and lcd output on Allwinner sunxi SoCs, lcd output
 requires the CONFIG_VIDEO_LCD_MODE Kconfig value to be set.
 
-The sunxi u-boot driver supports the following video-mode options:
+The sunxi U-Boot driver supports the following video-mode options:
 
 - monitor=[none|dvi|hdmi|lcd|vga|composite-*] - Select the video output to use
  none:     Disable video output.