We reserve space in the GuC workqueue for submitting the request in the
future. However, if we fail to construct the request, we need to give
that reserved space back to the system.

Fixes: dadd481b ("drm/i915/guc: Prepare for nonblocking execbuf submission")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97978Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: NMichał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161007065327.24515-4-chris@chris-wilson.co.uk