dmaengine: dw-axi-dmac: do not print NULL LLI during error

In the Linux kernel, the following vulnerability has been resolved: dmaengine: dw-axi-dmac: do not print NULL LLI during error During debugging we have seen an issue where axi_chan_dump_lli() is passed a NULL LLI pointer which ends up causing an OOPS due to trying to get fields from it. Simply print NULL LLI and exit to avoid this.