binman: Fix SyntaxWarning: invalid escape sequence '\('

Reproduct warning:

    $ git clean -dfx
    $ make CROSS_COMPILE="" qemu-x86_64_defconfig
    $ make -j8
    ...
    u-boot/tools/binman/etype/section.py:25:
    SyntaxWarning: invalid escape sequence '\('
    """Entry that contains other entries

Signed-off-by: Rong Tao <rongtao@cestc.cn>
1 file changed