Making corrections to PhD application after submitting it
This is not a material error. I wouldn't worry about it. We get much more egregious errors such as uploading the wrong statement (such as for another school) or misspelling the name of the core faculty member you wanted to work with, etc. 

You'd think those types of mistakes would be killer, but they really aren't. We realize students are under stress and that application management systems are cumbersome. We're all human in the end.

What's most important is the qualifications of the applicant as a whole.