ALSA: firewire-motu: mark trace helpers as __maybe_unused

Two functions were introduced for the purpose of tracing but cause warnings
when tracing is disabled:

sound/firewire/motu/amdtp-motu.c:284:13: error: 'copy_message' defined but not used [-Werror=unused-function]
 static void copy_message(u64 *frames, __be32 *buffer, unsigned int data_blocks,
sound/firewire/motu/amdtp-motu.c:271:13: error: 'copy_sph' defined but not used [-Werror=unused-function]
 static void copy_sph(u32 *frames, __be32 *buffer, unsigned int data_blocks,

Marking them as __maybe_unused will do the right thing here.

Fixes: 17909c1b ("ALSA: firewire-motu: add tracepoints for SPH in IEC 61883-1 fashion")
Fixes: c6b0b9e6 ("ALSA: firewire-motu: add tracepoints for messages for unique protocol")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/motu/amdtp-motu.c

@@ -268,8 +268,9 @@ static void read_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 }
 
 /* For tracepoints. */
-static void copy_sph(u32 *frames, __be32 *buffer, unsigned int data_blocks,
-		     unsigned int data_block_quadlets)
+static void __maybe_unused copy_sph(u32 *frames, __be32 *buffer,
+				    unsigned int data_blocks,
+				    unsigned int data_block_quadlets)
 {
 	unsigned int i;
 
@@ -281,8 +282,9 @@ static void copy_sph(u32 *frames, __be32 *buffer, unsigned int data_blocks,
 }
 
 /* For tracepoints. */
-static void copy_message(u64 *frames, __be32 *buffer, unsigned int data_blocks,
-			 unsigned int data_block_quadlets)
+static void __maybe_unused copy_message(u64 *frames, __be32 *buffer,
+					unsigned int data_blocks,
+					unsigned int data_block_quadlets)
 {
 	unsigned int i;