i2c: mxs: handle spurious interrupt

After an error interrupt setting cmd->err, I see another interrupt that
the data engine is empty which clears cmd->err before being processed.
So, clear cmd->err at the beginning of a transfer only to handle these
consecutive interrupts.
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

drivers/i2c/busses/i2c-mxs.c

@@ -227,6 +227,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 		return -EINVAL;
 
 	init_completion(&i2c->cmd_complete);
+	i2c->cmd_err = 0;
 
 	flags = stop ? MXS_I2C_CTRL0_POST_SEND_STOP : 0;
 
@@ -299,8 +300,6 @@ static irqreturn_t mxs_i2c_isr(int this_irq, void *dev_id)
 		    MXS_I2C_CTRL1_SLAVE_STOP_IRQ | MXS_I2C_CTRL1_SLAVE_IRQ))
 		/* MXS_I2C_CTRL1_OVERSIZE_XFER_TERM_IRQ is only for slaves */
 		i2c->cmd_err = -EIO;
-	else
-		i2c->cmd_err = 0;
 
 	is_last_cmd = (readl(i2c->regs + MXS_I2C_QUEUESTAT) &
 		MXS_I2C_QUEUESTAT_WRITE_QUEUE_CNT_MASK) == 0;