firewire: move rcode_string() to core

There is nothing audio-specific about the rcode_string() helper, so move
it from snd-firewire-lib into firewire-core to allow other code to use it.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (fixed sound/firewire/cmp.c)
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 0a19057..584826b 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -334,6 +334,7 @@
 int fw_run_transaction(struct fw_card *card, int tcode, int destination_id,
 		       int generation, int speed, unsigned long long offset,
 		       void *payload, size_t length);
+const char *fw_rcode_string(int rcode);
 
 static inline int fw_stream_packet_destination_id(int tag, int channel, int sy)
 {