media: mtk-jpeg: cancel workqueue on release for supported platforms only

In the Linux kernel, the following vulnerability has been resolved: media: mtk-jpeg: cancel workqueue on release for supported platforms only Since a recent fix the mtk_jpeg_release function cancels any pending or running work present in the driver workqueue using cancel_work_sync function. Currently, only the multicore based variants use this workqueue and they have the jpeg_worker platform data field initialized with a workqueue callback function. For the others, this field value remain NULL by default. The cancel_work_sync function is unconditionally called in mtk_jpeg_release function, even for the variants that do not use the workqueue. This call generates a WARN_ON print in __flush_work because the workqueue callback function presence check fails in __flush_work function (used by cancel_work_sync). So, to avoid these warnings, call cancel_work_sync only if a workqueue callback is defined in platform data.