drivers/gpu/drm/i915/selftests/i915_selftest.c: fix build with gcc-4.4.4

drivers/gpu/drm/i915/selftests/i915_selftest.c: fix build with gcc-4.4.4

gcc-4.4.4 has issues with anonymous union initializers.

In file included from drivers/gpu/drm/i915/selftests/i915_selftest.c:68:
drivers/gpu/drm/i915/selftests/i915_mock_selftests.h:11: error: unknown field 'mock' specified in initializer
drivers/gpu/drm/i915/selftests/i915_mock_selftests.h:11: warning: missing braces around initializer
drivers/gpu/drm/i915/selftests/i915_mock_selftests.h:11: warning: (near initialization for 'mock_selftests[0].<anonymous>')
drivers/gpu/drm/i915/selftests/i915_mock_selftests.h:12: error: unknown field 'mock' specified in initializer
drivers/gpu/drm/i915/selftests/i915_mock_selftests.h:13: error: unknown field 'm
...

Work around this.

Fixes: 953c7f82eb89 ("drm/i915: Provide a hook for selftests")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170310090314.3142-1-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>