i965/gen8+: Remove redundant zeroing of surface state

i965/gen8+: Remove redundant zeroing of surface state

The allocate_surface_state already zeroes out the surface state, and doing it
later in the function is destructive for what we want to accomplish when we
split out support for gen9 fast clears (next patch).

NOTE: Only dword 12 actually needed to be fixed, but it seemed more consistent
to remove the other instances as well. I can make an argument both ways (open
coding it, vs. not). I can rework the next patch if requires.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chad Versace <chad.versace@intel.com>
Reviewed-by: Neil Roberts <neil@linux.intel.com>