i965: fix typo

i965: fix typo

Noticed by clang:

brw_wm_surface_state.c:330:30: warning: initializer overrides prior
initialization of this subobject [-Winitializer-overrides]
      [MESA_FORMAT_Z24_S8] = 0,
                             ^
brw_wm_surface_state.c:326:30: note: previous initialization is here
      [MESA_FORMAT_Z24_S8] = 0,
                             ^

No functionality change, since the array is declared static so
it was zero-initialized by default.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>