tracing: Pass export pointer as argument to ->write()

By passing an export descriptor to the write function, users don't need to
keep a global static pointer and can rely on container_of() to fetch their
own structure.

Link: http://lkml.kernel.org/r/20170602102025.5140-1-felipe.balbi@linux.intel.com

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
diff --git a/drivers/hwtracing/stm/ftrace.c b/drivers/hwtracing/stm/ftrace.c
index bd126a7..7da7564 100644
--- a/drivers/hwtracing/stm/ftrace.c
+++ b/drivers/hwtracing/stm/ftrace.c
@@ -42,9 +42,11 @@ static struct stm_ftrace {
  * @len:	length of the data packet
  */
 static void notrace
-stm_ftrace_write(const void *buf, unsigned int len)
+stm_ftrace_write(struct trace_export *export, const void *buf, unsigned int len)
 {
-	stm_source_write(&stm_ftrace.data, STM_FTRACE_CHAN, buf, len);
+	struct stm_ftrace *stm = container_of(export, struct stm_ftrace, ftrace);
+
+	stm_source_write(&stm->data, STM_FTRACE_CHAN, buf, len);
 }
 
 static int stm_ftrace_link(struct stm_source_data *data)