ALSA: firewire: introduce amdtp_out_stream_running()

Introduce the helper function amdtp_out_stream_running().  This makes
many checks in amdtp.c clearer and frees the device drivers from having
to track this with a separate variable.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index efb2e29..d56b8e7 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -59,7 +59,7 @@
  */
 void amdtp_out_stream_destroy(struct amdtp_out_stream *s)
 {
-	WARN_ON(!IS_ERR(s->context));
+	WARN_ON(amdtp_out_stream_running(s));
 	mutex_destroy(&s->mutex);
 	fw_unit_put(s->unit);
 }
@@ -89,7 +89,7 @@
 	};
 	unsigned int sfc;
 
-	if (WARN_ON(!IS_ERR(s->context)))
+	if (WARN_ON(amdtp_out_stream_running(s)))
 		return;
 
 	for (sfc = 0; sfc < ARRAY_SIZE(rate_info); ++sfc)
@@ -145,7 +145,7 @@
 void amdtp_out_stream_set_pcm_format(struct amdtp_out_stream *s,
 				     snd_pcm_format_t format)
 {
-	if (WARN_ON(!IS_ERR(s->context)))
+	if (WARN_ON(amdtp_out_stream_running(s)))
 		return;
 
 	switch (format) {
@@ -481,7 +481,7 @@
 
 	mutex_lock(&s->mutex);
 
-	if (WARN_ON(!IS_ERR(s->context) ||
+	if (WARN_ON(amdtp_out_stream_running(s) ||
 		    (!s->pcm_channels && !s->midi_ports))) {
 		err = -EBADFD;
 		goto err_unlock;
@@ -577,7 +577,7 @@
 {
 	mutex_lock(&s->mutex);
 
-	if (IS_ERR(s->context)) {
+	if (!amdtp_out_stream_running(s)) {
 		mutex_unlock(&s->mutex);
 		return;
 	}