i965/fs: Make scratch write instructions use the correct execution size

Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
diff --git a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
index c017137..2313af9 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
@@ -732,7 +732,7 @@
    for (int i = 0; i < count / reg_size; i++) {
       fs_inst *spill_inst =
          new(mem_ctx) fs_inst(SHADER_OPCODE_GEN4_SCRATCH_WRITE,
-                              reg_null_f, src);
+                              reg_size * 8, reg_null_f, src);
       src.reg_offset += reg_size;
       spill_inst->offset = spill_offset + i * reg_size * REG_SIZE;
       spill_inst->ir = inst->ir;