drm/i915/guc: Don't pass CTB while writing

drm/i915/guc: Don't pass CTB while writing

Since we only have one SEND buffer we don't need to explicitly pass
it to the write function.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200117082039.65644-3-michal.wajdeczko@intel.com