dmaengine: pl330: Demote obvious misuse of kerneldoc to standard comment block

No 'struct' title is provided.  Nor are any attribute descriptions.

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

 drivers/dma/pl330.c:295: warning: cannot understand function prototype: 'struct pl330_reqcfg '

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Jaswinder Singh <jassi.brar@samsung.com>
Link: https://lore.kernel.org/r/20200714111546.1755231-6-lee.jones@linaro.org


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