drm/i915: Remove extraneous request cancel.

Remove extraneous request cancel in request allocation failure path
in intel_lr_context_deferred_alloc (Tvrtko Ursulin)

Regression from:

  commit e84fe803


  Author: Nick Hoath <nicholas.hoath@intel.com>
  Date:   Fri Sep 11 12:53:46 2015 +0100

      drm/i915: Split alloc from init for lrc

Signed-off-by: Nick Hoath <nicholas.hoath@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>