binman: fix default filename of u-boot-with-ucode-ptr in documentation

The suffix should be ".bin" instead of ".dtb" .

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed