drm/i915/guc: work around gcc-4.4.4 union initializer issue

gcc-4.4.4 has problems with initalizers of anon unions.

drivers/gpu/drm/i915/intel_guc_log.c: In function 'guc_log_control':
drivers/gpu/drm/i915/intel_guc_log.c:64: error: unknown field 'logging_enabled' specified in initializer

Work around this.

Fixes: 35fe703c

 ("drm/i915/guc: Change values for i915_guc_log_control")
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180308001333.rI2vrNRTY%akpm@linux-foundation.org