amd/common: Always initialize gfx9 mipmap offset/pitch.

amd/common: Always initialize gfx9 mipmap offset/pitch.

The WSI expects pitch to be meaningful even for tiled
textures.

(It is used for the pitch in modesetting and X11)

Fixes: 824bd0830e8 "radv: return the correct pitch for linear mipmaps on GFX10"
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2301
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2304
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3245>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3245>