drm/i915/gt: Mark up virtual engine uabi_instance

Be sure to initialise the uabi_instance on the virtual engine to the
special invalid value, just in case we ever peek at it from the uAPI.
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 750e76b4 ("drm/i915/gt: Move the [class][inst] lookup for engines onto the GT")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.4+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200106123921.2543886-1-chris@chris-wilson.co.uk
(cherry picked from commit f75fc37b)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -4416,9 +4416,11 @@ intel_execlists_create_virtual(struct i915_gem_context *ctx,
 	ve->base.gt = siblings[0]->gt;
 	ve->base.uncore = siblings[0]->uncore;
 	ve->base.id = -1;
+
 	ve->base.class = OTHER_CLASS;
 	ve->base.uabi_class = I915_ENGINE_CLASS_INVALID;
 	ve->base.instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;
+	ve->base.uabi_instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;
 
 	/*
 	 * The decision on whether to submit a request using semaphores