mtmd: read the MiniCPM-V projection width from ne[1] (#32132)
The MiniCPM-V resampler ends with build_mm(mm_model_proj), whose output
width is ne[1], while n_mmproj_embd() returns ne[0]. Both are equal in
real models, the projection is square. A non square projection passes
the text model n_embd check and only aborts at the encode, on the
output buffer size check.
Return ne[1], so the width matches the graph output.
