i2c: i2c-mxs: Use DMA mode even for small transfers

Recently we have been seing some reports about PIO mode not working properly.

- http://www.spinics.net/lists/linux-i2c/msg11985.html
- http://marc.info/?l=linux-i2c&m=137235593101385&w=2
- https://lkml.org/lkml/2013/6/24/430

Let's use DMA mode even for small transfers.

Without this patch, i2c reads the incorrect sgtl5000 version on a mx28evk when
touchscreen is enabled:

[    5.856270] sgtl5000 0-000a: Device with ID register 0 is not a sgtl5000
[    9.877307] sgtl5000 0-000a: ASoC: failed to probe CODEC -19
[    9.883528] mxs-sgtl5000 sound.12: ASoC: failed to instantiate card -19
[    9.892955] mxs-sgtl5000 sound.12: snd_soc_register_card failed (-19)

Cc: <stable@vger.kernel.org>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Marek Vasut <marex@denx.de>

[wsa: we have a proper solution for -next, so this non intrusive
solution is OK for now]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-mxs.c

@@ -493,7 +493,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 	 * based on this empirical measurement and a lot of previous frobbing.
 	 */
 	i2c->cmd_err = 0;
-	if (msg->len < 8) {
+	if (0) {	/* disable PIO mode until a proper fix is made */
 		ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
 		if (ret)
 			mxs_i2c_reset(i2c);