nvme: use better description for async reset reason

The NVMe AER notification of a persistent internal error triggers a
reset. The existing warning message just says "due to AER", which can be
confused with the unrelated PCIe AER condition. Just say what the event
was instead of the generic overloaded acronym.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>