mfd: wm97xx-core: Platform data can be NULL

It is not mandatory that platform data is passed along the ac97
codec. Actually there are configuration without a battery connected to
the ADC of the codec.

This is for example the case for the PXA zylonite platform, so fix the
NULL dereferencing by adding a test.

Fixes: a5c6951c49fb ("mfd: wm97xx-core: core support for wm97xx Codec")
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/wm97xx-core.c

@@ -278,7 +278,7 @@ static int wm97xx_ac97_probe(struct ac97_codec_device *adev)
 
 	codec_pdata = &wm97xx->codec_pdata;
 	codec_pdata->ac97 = wm97xx->ac97;
-	codec_pdata->batt_pdata = pdata->batt_pdata;
+	codec_pdata->batt_pdata = pdata ? pdata->batt_pdata : NULL;
 
 	switch (adev->vendor_id) {
 	case WM9705_VENDOR_ID: