drm: fix allowing master ioctls on non-master fds.

The multi-master patches changed master to a pointer, and this fell out,
change to use is_master.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_drv.c

@@ -493,7 +493,7 @@ int drm_ioctl(struct inode *inode, struct file *filp,
 		retcode = -EINVAL;
 	} else if (((ioctl->flags & DRM_ROOT_ONLY) && !capable(CAP_SYS_ADMIN)) ||
 		   ((ioctl->flags & DRM_AUTH) && !file_priv->authenticated) ||
-		   ((ioctl->flags & DRM_MASTER) && !file_priv->master)) {
+		   ((ioctl->flags & DRM_MASTER) && !file_priv->is_master)) {
 		retcode = -EACCES;
 	} else {
 		if (cmd & (IOC_IN | IOC_OUT)) {