Does an mri result of "minimal nonspecific periventricular deep white matter intensities" correlate or rule out an autism diagnosis in a 3yr old girl?

No: The word 'non-specific' is the important one here, meaning that the 'deep white matter intensities' do not of themselves yield a diagnosis.

Not correlation: Should discuss with the neurologist on what it likely represents . But I can tell you it is not known to have a significant correlation with autism by itself e.g this finding is a well established determinant one way or another is not so. Take care.