i965: Use brw_batch_references in tex_busy check

i965: Use brw_batch_references in tex_busy check

If the batch references the buffer, we will have to flush the batch
immediately before mapping it, at which point it will be busy.

(This bug has existed for a long time...even going back to BLT-era...)

Fixes: 779923194c6 ("i965/tex_image: Use meta for instead of the blitter PBO TexImage and GetTexImage")
Fixes: d5d4ba9139a ("i965/tex_subimage: use meta instead of the blitter for PBO TexSubImage")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3616>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3616>