firewire: core: fulfill documentation of fw_iso_context_flush_completions()

The fw_iso_context_flush_completions() is the counterpart of
fw_iso_context_schedule_work() to process isochronous context in current
process context.

This commit fulfills its documentation.

Link: https://lore.kernel.org/r/20240908040549.75304-3-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-iso.c

@@ -209,6 +209,17 @@ void fw_iso_context_queue_flush(struct fw_iso_context *ctx)
 }
 EXPORT_SYMBOL(fw_iso_context_queue_flush);
 
+/**
+ * fw_iso_context_flush_completions() - process isochronous context in current process context.
+ * @ctx: the isochronous context
+ *
+ * Process the isochronous context in the current process context. The registered callback function
+ * is called if some packets have been already transferred since the last time. If it is required
+ * to process the context asynchronously, fw_iso_context_schedule_flush_completions() is available
+ * instead.
+ *
+ * Context: Process context. May sleep due to disable_work_sync().
+ */
 int fw_iso_context_flush_completions(struct fw_iso_context *ctx)
 {
 	int err;