ALSA: firewire-lib: fix wrong value as length of header for CIP_NO_HEADER case

In a commit 1d717123bb ("ALSA: firewire-lib: Avoid
-Wflex-array-member-not-at-end warning"), DEFINE_FLEX() macro was used to
handle variable length of array for header field in struct fw_iso_packet
structure. The usage of macro has a side effect that the designated
initializer assigns the count of array to the given field. Therefore
CIP_HEADER_QUADLETS (=2) is assigned to struct fw_iso_packet.header,
while the original designated initializer assigns zero to all fields.

With CIP_NO_HEADER flag, the change causes invalid length of header in
isochronous packet for 1394 OHCI IT context. This bug affects all of
devices supported by ALSA fireface driver; RME Fireface 400, 800, UCX, UFX,
and 802.

This commit fixes the bug by replacing it with the alternative version of
macro which corresponds no initializer.

Cc: stable@vger.kernel.org
Fixes: 1d717123bb ("ALSA: firewire-lib: Avoid -Wflex-array-member-not-at-end warning")
Reported-by: Edmund Raile <edmund.raile@proton.me>
Closes: https://lore.kernel.org/r/rrufondjeynlkx2lniot26ablsltnynfaq2gnqvbiso7ds32il@qk4r6xps7jh2/
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20240725155640.128442-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

sound/firewire/amdtp-stream.c

@@ -1180,8 +1180,7 @@ static void process_rx_packets(struct fw_iso_context *context, u32 tstamp, size_
 		(void)fw_card_read_cycle_time(fw_parent_device(s->unit)->card, &curr_cycle_time);
 
 	for (i = 0; i < packets; ++i) {
-		DEFINE_FLEX(struct fw_iso_packet, template, header,
-			    header_length, CIP_HEADER_QUADLETS);
+		DEFINE_RAW_FLEX(struct fw_iso_packet, template, header, CIP_HEADER_QUADLETS);
 		bool sched_irq = false;
 
 		build_it_pkt_header(s, desc->cycle, template, pkt_header_length,