i965: Actually check every primitive for cut index support.

i965: Actually check every primitive for cut index support.

can_cut_index_handle_prims() was passed an array of _mesa_prim objects
and a count, and ran a loop for that many iterations.  However, it
treated the array like a pointer, repeatedly checking the first element.

This patch makes it actually check every primitive.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>