A zero MBR disk signature is generally seen as no signature and
another partitioning program might install a new signature.
(From OE-Core rev: b6cafb1fcd6c168f8f4a4d2d5c74f3b425f156f3)
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>