dmaengine: xilinx_dma: fix xilinx_dma_child_probe() return documentation

Modify xilinx_dma_child_probe() return documentation to be inline
with implementation i.e. can also return failure value on error.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://lore.kernel.org/r/1666683737-7668-2-git-send-email-radhey.shyam.pandey@amd.com


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