i965/cs: Use exec all for CS terminate

This prevents an assertion from being hit with SIMD16:

Assertion `inst->exec_size == dispatch_width() || force_writemask_all' failed.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/mesa/drivers/dri/i965/brw_fs_visitor.cpp

@@ -1948,7 +1948,8 @@ fs_visitor::emit_cs_terminate()
    bld.exec_all().MOV(payload, g0);
 
    /* Send a message to the thread spawner to terminate the thread. */
-   fs_inst *inst = bld.emit(CS_OPCODE_CS_TERMINATE, reg_undef, payload);
+   fs_inst *inst = bld.exec_all()
+                      .emit(CS_OPCODE_CS_TERMINATE, reg_undef, payload);
    inst->eot = true;
 }