usb: phy: mxs: suspend to RAM causes NULL pointer dereference

Triggering suspend to RAM via sysfs on a i.MX28 causes a NULL pointer
dereference. This patch avoids the oops in mxs_phy_get_vbus_status()
by aborting since there is no syscon available.
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Fixes: efdbd3a5 ("usb: phy: mxs: do not set PWD.RXPWD1PT1 for low speed connection")
CC: <stable@vger.kernel.org> # 4.0
Acked-by: NPeter Chen <peter.chen@freescale.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/phy/phy-mxs-usb.c

@@ -217,6 +217,9 @@ static bool mxs_phy_get_vbus_status(struct mxs_phy *mxs_phy)
 {
 	unsigned int vbus_value;
 
+	if (!mxs_phy->regmap_anatop)
+		return false;
+
 	if (mxs_phy->port_id == 0)
 		regmap_read(mxs_phy->regmap_anatop,
 			ANADIG_USB1_VBUS_DET_STAT,