fsldma: remove useless use of lock

Accordingly to dma_cookie_status() description locking is not required.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Li Yang <leoli@freescale.com>
Cc: Zhang Wei <zw@zh-kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Vinod Koul <vinod.koul@intel.com>