dmaengine: remove ste_dma40 from issue_pending TODO

ste_dma40 now implements issue_pending according to documentation.
Submit adds descriptos to a pending queue with are flushed down to the DMAC
at issue_pending.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>