dmaengine: at_hdmac: fix some kernel-doc warnings

dmaengine: at_hdmac: fix some kernel-doc warnings

Fix some kernel-doc format warnings:

at_hdmac.c:243: warning: Excess struct member 'sg_len' description in 'at_desc'
at_hdmac.c:252: warning: cannot understand function prototype: 'enum atc_status '
ez
at_hdmac.c:351: warning: Excess struct member 'atdma_devtype' description in 'at_dma'
at_hdmac.c:351: warning: Excess struct member 'ch_regs' description in 'at_dma'
at_hdmac.c:664: warning: contents before sections

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Link: https://lore.kernel.org/r/20240121070021.25365-1-rdunlap@infradead.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>