staging/android: rename 'sync_pt' to 'fence' in struct sync_fence_cb

'sync_pt' is actually declared as struct fence so to make the name means
its type we rename it to 'fence'.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>