ALSA: sound/ppc/powermac: remove undefined operations

Modifying an object twice without an intervening sequence point is
undefined.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/ppc/tumbler.c b/sound/ppc/tumbler.c
index 20afdf9..961d982 100644
--- a/sound/ppc/tumbler.c
+++ b/sound/ppc/tumbler.c
@@ -785,7 +785,7 @@
 	if (! mix->i2c.client)
 		return -ENODEV;
 	if (mix->capture_source)
-		mix->acs = mix->acs |= 2;
+		mix->acs |= 2;
 	else
 		mix->acs &= ~2;
 	return i2c_smbus_write_byte_data(mix->i2c.client, TAS_REG_ACS, mix->acs);