This patch fixes the sanity check on the non-secure entrypoint value
returned by bl31_plat_get_next_image_ep_info(). This issue has been
reported by Coverity Scan Online:

  CID 264893 (#1 of 1): Dereference null return value (NULL_RETURNS)
  Dereferencing a null pointer ns_ep_info.

Change-Id: Ia0f64d8c8b005f042608f1422ecbd42bc90b2fb4
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>