radeonsi: initialise imported surface to 0.

radeonsi: initialise imported surface to 0.

For memobj imports we weren't setting the surface to 0, which
meant sometimes we'd end up with tile_swizzle garbage, which
would corrupt rendering.

This seems to fix the image corruption on the imported memory
objects in vrdashboard for me.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>