Fix a mistake sentence in the file 'Documentation/zh_CN/magic-number.txt'

This is a patch for correcting a mistake sentence in the file
Documentation/zh_CN/magic-number.txt.

signed-off-by: Harry Wei <harryxiyou@gmail.com>
Reported-by: Zhang Shuanglong <zhangsl16@gmail.com>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>