i965/fs: Fix gl_SampleMask handling for SIMD16 on Gen8+.

We actually want to use mov(16), not mov(8).

Fixes 7 Piglit tests: ARB_sample_shading/builtin-gl-sample-mask [2468]
and ARB_sample_shading/builtin-gl-sample-mask-simple [468].

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80991
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>

src/mesa/drivers/dri/i965/gen8_fs_generator.cpp

@@ -715,13 +715,8 @@ gen8_fs_generator::generate_set_omask(fs_inst *inst,
              mask.hstride == BRW_HORIZONTAL_STRIDE_0);
    }
 
-   unsigned save_exec_size = default_state.exec_size;
-   default_state.exec_size = BRW_EXECUTE_8;
-
    gen8_instruction *mov = MOV(dst, retype(mask, dst.type));
    gen8_set_mask_control(mov, BRW_MASK_DISABLE);
-
-   default_state.exec_size = save_exec_size;
 }
 
 /**