ASoC: simple-card-utils: Fix pointer check in graph_util_parse_link_direction

In the Linux kernel, the following vulnerability has been resolved: ASoC: simple-card-utils: Fix pointer check in graph_util_parse_link_direction Actually check if the passed pointers are valid, before writing to them. This also fixes a USBAN warning: UBSAN: invalid-load in ../sound/soc/fsl/imx-card.c:687:25 load of value 255 is not a valid value for type '_Bool' This is because playback_only is uninitialized and is not written to, as the playback-only property is absent.