ASoC: Fix mpc5200-psc-ac97 to ensure the data ready bit is cleared

When doing register reads, it is possible for there to be a stale
data ready bit set which will cause subsequent reads to return
prematurely with incorrect data.  This patch fixes the issues by
ensuring stale data is cleared before starting another transaction.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Jon Smirl <jonsmirl@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/fsl/mpc5200_psc_ac97.c

@@ -41,6 +41,10 @@ static unsigned short psc_ac97_read(struct snd_ac97 *ac97, unsigned short reg)
 		pr_err("timeout on ac97 bus (rdy)\n");
 		return -ENODEV;
 	}
+
+	/* Force clear the data valid bit */
+	in_be32(&psc_dma->psc_regs->ac97_data);
+
 	/* Send the read */
 	out_be32(&psc_dma->psc_regs->ac97_cmd, (1<<31) | ((reg & 0x7f) << 24));