ALSA: echoaudio: Fix memory allocation

commit 9c6795a9 upstream.

'commpage_bak' is allocated with 'sizeof(struct echoaudio)' bytes.
We then copy 'sizeof(struct comm_page)' bytes in it.
On my system, smatch complains because one is 2960 and the other is 3072.

This would result in memory corruption or a oops.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

sound/pci/echoaudio/echoaudio.c

@@ -2253,11 +2253,11 @@ static int snd_echo_resume(struct device *dev)
 
 	DE_INIT(("resume start\n"));
 	pci_restore_state(pci);
-	commpage_bak = kmalloc(sizeof(struct echoaudio), GFP_KERNEL);
+	commpage_bak = kmalloc(sizeof(*commpage), GFP_KERNEL);
 	if (commpage_bak == NULL)
 		return -ENOMEM;
 	commpage = chip->comm_page;
-	memcpy(commpage_bak, commpage, sizeof(struct comm_page));
+	memcpy(commpage_bak, commpage, sizeof(*commpage));
 
 	err = init_hw(chip, chip->pci->device, chip->pci->subsystem_device);
 	if (err < 0) {