nvme: fix two discard related issues
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2174443
The 1st patch fixes warning in nvme_setup_discard() caused by single max discard
segment, which isn't supported by current nvme stack, however there is really
such nvme device.
The 2nd patch fixes discard report from hardware.
Signed-off-by: Ming Lei ming.lei@redhat.com