dma: edma: fix incorrect SG list handling

The code to handle any length SG lists calls edma_resume()
even before edma_start() is called. This is incorrect
because edma_resume() enables edma events on the channel
after which CPU (in edma_start) cannot clear posted
events by writing to ECR (per the EDMA user's guide).

Because of this EDMA transfers fail to start if due
to some reason there is a pending EDMA event registered
even before EDMA transfers are started. This can happen if
an EDMA event is a byproduct of device initialization.

Fix this by calling edma_resume() only if it is not the
first batch of MAX_NR_SG elements.

Without this patch, MMC/SD fails to function on DA850 EVM
with DMA. The behaviour is triggered by specific IP and
this can explain why the issue was not reported before
(example with MMC/SD on AM335x).

Tested on DA850 EVM and AM335x EVM-SK using MMC/SD card.

Cc: [email protected] # v3.12.x+
Cc: Joel Fernandes <[email protected]>
Acked-by: Joel Fernandes <[email protected]>
Tested-by: Jon Ringle <[email protected]>
Tested-by: Alexander Holler <[email protected]>
Reported-by: Jon Ringle <[email protected]>
Signed-off-by: Sekhar Nori <[email protected]>
Signed-off-by: Vinod Koul <[email protected]>

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