dmaengine: xgene-dma: Provide descriptions for 'dev' and 'clk' in device's ddata

dmaengine: xgene-dma: Provide descriptions for 'dev' and 'clk' in device's ddata

Fixes the following W=1 kernel build warning(s):

 drivers/dma/xgene-dma.c:310: warning: Function parameter or member 'dev' not described in 'xgene_dma'
 drivers/dma/xgene-dma.c:310: warning: Function parameter or member 'clk' not described in 'xgene_dma'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Prasad Sahu <rsahu@apm.com>
Cc: Loc Ho <lho@apm.com>
Link: https://lore.kernel.org/r/20200714111546.1755231-15-lee.jones@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>