dmaengine: at_xdmac: In at_xdmac_prep_dma_memset, treat value as a single byte

The value passed in to .prep_dma_memset is to be treated as a single
byte repeating pattern.

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20220301182551.883474-4-benjamin.walker@intel.com


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