synclink_gt fix locking in error path of rx enable

Fix locking in error path of rx_enable() introduced by
synclink_gt-add-rx-dma-buffer-fill-level-control patch.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>