drm/i915: Update ifdeffery for mutex->owner

In commit 7608a43d ("locking/mutexes: Use MUTEX_SPIN_ON_OWNER when
appropriate") the owner field in the mutex was updated from being
dependent upon CONFIG_SMP to using optimistic spin. Update our peek
function to suite.

Fixes:7608a43d

 ("locking/mutexes: Use MUTEX_SPIN_ON_OWNER...")
Reported-by: Hong Liu <hong.liu@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1468244777-4888-1-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>