dmaengine: dw-edma: Change DMA abbreviation from lower into upper case

To keep code consistent, some comments with dma keyword written in lower
case are now in upper case.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Link: https://lore.kernel.org/r/8c4b3db90767972a2b4cbb6fa818cf0e9c3d6fe3.1613674948.git.gustavo.pimentel@synopsys.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>