radeonsi: fix surf_pitch for subsampled surface

radeonsi: fix surf_pitch for subsampled surface

gfx9.surf_pitch is supposed to be in blocks (or elements) but addrlib
returns a pitch in pixels.
This cause a mismatch between surface->bpe and surface.u.gfx9.surf_pitch.

For subsampled formats like uyvy (bpe is 2) this breaks in various places:
 - sdma copy
 - video rendering (see issue https://gitlab.freedesktop.org/mesa/mesa/issues/2363)
   when the vl_compositor_gfx_render method is used

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3738>