Sandisk SSDs SD7SN6S256G and SD8SN8U256G are regularly locking up
regularly under sustained moderate load with NCQ enabled.  Blacklist
for now.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NDave Jones <davej@codemonkey.org.uk>
Cc: stable@vger.kernel.org