document xilinx_dma_device_config() return value. Fixes below
kernel-doc warning.

xilinx_dma.c:1665: warning: No description found for return value
of 'xilinx_dma_device_config'
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://lore.kernel.org/r/1666683737-7668-3-git-send-email-radhey.shyam.pandey@amd.comSigned-off-by: Vinod Koul <vkoul@kernel.org>