dma: mmp_pdma: don't clear DCMD_ENDIRQEN at end of pending chain

In order to fully support multiple transactions per channel, we need to
assure we get an interrupt for each completed transaction. That flags
bit is also our only way to tell at which descriptor a transaction ends.

So, remove the manual clearing of that bit, and then inline the only
remaining command that is left in append_pending_queue() for better
readability.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>