agp: remove uid comparison as security check

In the face of containers and user namespaces, a uid==0 check for
security is not safe.  Switch to a capability check.

I'm not sure I picked the right capability, but this being AGP
CAP_SYS_RAWIO seemed to make sense.

Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/agp/frontend.c

@@ -689,7 +689,7 @@ static int agp_open(struct inode *inode, struct file *file)
 	set_bit(AGP_FF_ALLOW_CLIENT, &priv->access_flags);
 	priv->my_pid = current->pid;
 
-	if ((current->uid == 0) || (current->suid == 0)) {
+	if (capable(CAP_SYS_RAWIO)) {
 		/* Root priv, can be controller */
 		set_bit(AGP_FF_ALLOW_CONTROLLER, &priv->access_flags);
 	}