isl: Drop misplaced comment about padding

isl: Drop misplaced comment about padding

isl has a giant comment that explains the hardware's padding
requirements. (Hint: Cache lines and page faults). But the comment is in
the wrong place, in isl_calc_linear_row_pitch(), which is unrelated to
padding.

The important parts of that comment were copied to
isl_apply_surface_padding() long ago. So drop the misplaced comment.

Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>