i965/vec4: fix size_written for doubles

Reviewed-by: Matt Turner <mattst88@gmail.com>
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index e88bb7c..0bf423c 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -46,7 +46,6 @@
    this->predicate = BRW_PREDICATE_NONE;
    this->predicate_inverse = false;
    this->target = 0;
-   this->size_written = (dst.file == BAD_FILE ? 0 : REG_SIZE);
    this->shadow_compare = false;
    this->ir = NULL;
    this->urb_write_flags = BRW_URB_WRITE_NO_FLAGS;
@@ -56,6 +55,8 @@
    this->base_mrf = 0;
    this->offset = 0;
    this->exec_size = 8;
+   this->size_written = (dst.file == BAD_FILE ?
+                         0 : this->exec_size * type_sz(dst.type));
    this->annotation = NULL;
 }