i965: Use WE_all for FB write header setup on Broadwell.

i965: Use WE_all for FB write header setup on Broadwell.

I forgot to disable writemasking on the OR and MOV which set the render
target index and "source 0 alpha present to render target" bit.

Using get_element_ud is equivalent and avoids a line-wrap.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>