ALSA: core: Fix unexpected error at replacing user TLV

BugLink: http://bugs.launchpad.net/bugs/1714298

commit 88c54cdf upstream.

When user tries to replace the user-defined control TLV, the kernel
checks the change of its content via memcmp().  The problem is that
the kernel passes the return value from memcmp() as is.  memcmp()
gives a non-zero negative value depending on the comparison result,
and this shall be recognized as an error code.

The patch covers that corner-case, return 1 properly for the changed
TLV.

Fixes: 8aa9b586 ("[ALSA] Control API - more robust TLV implementation")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

sound/core/control.c

@@ -1126,7 +1126,7 @@ static int snd_ctl_elem_user_tlv(struct snd_kcontrol *kcontrol,
 		mutex_lock(&ue->card->user_ctl_lock);
 		change = ue->tlv_data_size != size;
 		if (!change)
-			change = memcmp(ue->tlv_data, new_data, size);
+			change = memcmp(ue->tlv_data, new_data, size) != 0;
 		kfree(ue->tlv_data);
 		ue->tlv_data = new_data;
 		ue->tlv_data_size = size;