This patch fixes a bug in the 'file_to_uuid()' function: it used
to cause an exception by dereferencing a null pointer when
a given UUID was not found in the UUID array. The fix is to delete
the final null entry in the UUID array, which is not needed because
the array is statically declared so its size is known at build time.

Fixes ARM-software/tf-issues#43

Change-Id: I0a003485b88134564c0d36f57c274215d9e16532