[PATCHv2] NVMe: Fix reset/remove race

[Christoph Hellwig]

This looks ok:

Reviewed-by: Christoph Hellwig <hch at lst.de>

But this just shows we'll finally need a real state machine for the
NVMe controller instead of the flags.  Sagi did a really nice one
for the Fabrics driver, and I'll plan to lift it to common code for
4.7.