i965: do not emit empty surface state

i965: do not emit empty surface state

If called with an empty size, brw_emit_buffer_surface_state asserts.
We already have a dedicated helper for uploading nothing, so let's use
that instead.

Avoids an assert in
dEQP-GLES31.functional.shaders.opaque_type_indexing.ssbo.const_literal_vertex
when running a debug build of i965.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>