drm/cred: wrap task credential accesses in the drm driver.

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: David Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_fops.c

@@ -246,7 +246,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
 	memset(priv, 0, sizeof(*priv));
 	filp->private_data = priv;
 	priv->filp = filp;
-	priv->uid = current->euid;
+	priv->uid = current_euid();
 	priv->pid = task_pid_nr(current);
 	priv->minor = idr_find(&drm_minors_idr, minor_id);
 	priv->ioctl_count = 0;