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/include/configs/bf537-pnav.h b/include/configs/bf537-pnav.h
index 2474adb..5794f47 100644
--- a/include/configs/bf537-pnav.h
+++ b/include/configs/bf537-pnav.h
@@ -1,5 +1,5 @@
 /*
- * U-boot - Configuration file for BF537 PNAV board
+ * U-Boot - Configuration file for BF537 PNAV board
  */
 
 #ifndef __CONFIG_BF537_PNAV_H__