fsldma: Fix cookie issues

fsl_dma_tx_submit() only sets the cookie on the first descriptor of a
transaction. It should set the cookie on all.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Acked-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>