mesa/meta: move BindTexture() call in _mesa_meta_GenerateMipmap()

This is a follow-up to commit e3fa700c178e11e6735430119232919176ab7b42.

The call to _mesa_BindTexture() must be before we set any other texture
object state, namely the _mesa_TexParameteri() calls.

This fixes bug 25601 (piglit gen-nonzero-unit failure).
1 file changed