coverity: fix dereference NULL return value

also break once we have found root, no need to search the rest of the mounts

Changelog: May 6: Serge: don't add the break.  (see m-l)

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>