usb: typec: unlock dp->lock on error exit path, and also zero ret if successful

One of the error handling paths forgets to unlock dp->lock on the error
exit path leading to a potential lock-up.  Also the return path for a
successful call to the function configuration_store can return an
uninitialized error return code if dp->alt->active is false, so ensure
ret is zeroed on the successful exit path to avoid garbage being returned.

Detected by CoverityScan, CID#1471597 ("Unitialized scalar variable")

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/altmodes/displayport.c

@@ -333,7 +333,7 @@ configuration_store(struct device *dev, struct device_attribute *attr,
 	u32 conf;
 	u32 cap;
 	int con;
-	int ret;
+	int ret = 0;
 
 	con = sysfs_match_string(configurations, buf);
 	if (con < 0)
@@ -349,8 +349,10 @@ configuration_store(struct device *dev, struct device_attribute *attr,
 	cap = DP_CAP_CAPABILITY(dp->alt->vdo);
 
 	if ((con == DP_CONF_DFP_D && !(cap & DP_CAP_DFP_D)) ||
-	    (con == DP_CONF_UFP_D && !(cap & DP_CAP_UFP_D)))
-		return -EINVAL;
+	    (con == DP_CONF_UFP_D && !(cap & DP_CAP_UFP_D))) {
+		ret = -EINVAL;
+		goto err_unlock;
+	}
 
 	conf = dp->data.conf & ~DP_CONF_DUAL_D;
 	conf |= con;