[ALSA] Add MPU401_INFO_NO_ACK bitflag

Added MPU401_INFO_NO_ACK bitflag to ignore the ACK check for UART
commands.  VT172x doesn't handle ACK commands, for example.

Tested-by: Pavel Hofman <pavel.hofman@insite.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/mpu401/mpu401_uart.c b/sound/drivers/mpu401/mpu401_uart.c
index 18cca24..2af0999 100644
--- a/sound/drivers/mpu401/mpu401_uart.c
+++ b/sound/drivers/mpu401/mpu401_uart.c
@@ -243,7 +243,7 @@
 #endif
 	}
 	mpu->write(mpu, cmd, MPU401C(mpu));
-	if (ack) {
+	if (ack && !(mpu->info_flags & MPU401_INFO_NO_ACK)) {
 		ok = 0;
 		timeout = 10000;
 		while (!ok && timeout-- > 0) {