esp: apply transfer length adjustment when STC is zero at TC load time

esp: apply transfer length adjustment when STC is zero at TC load time

Perform the length adjustment whereby a value of 0 in the STC represents
a transfer length of 0x10000 at the point where the TC is loaded at the
start of a DMA command rather than just when a TI (Transfer Information)
command is executed. This better matches the description as given in the
datasheet.

Signed-off-by: Mark Cave-Ayland <[email protected]>
Reviewed-by: Laurent Vivier <[email protected]>
Message-Id: <20210304221103[email protected]>