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.qemu-mips b/doc/README.qemu-mips
index a192752..3940fac 100644
--- a/doc/README.qemu-mips
+++ b/doc/README.qemu-mips
@@ -157,7 +157,7 @@
 (gdb)  target remote localhost:1234
 Remote debugging using localhost:1234
 _start () at start.S:64
-64		RVECENT(reset,0)	/* U-boot entry point */
+64		RVECENT(reset,0)	/* U-Boot entry point */
 Current language:  auto; currently asm
 (gdb)  b board.c:289
 Breakpoint 1 at 0xbfc00cc8: file board.c, line 289.