nvme: Don't allow to reset a reconnecting controller

The reset operation is guaranteed to fail for all scenarios
but the esoteric case where in the last reconnect attempt
concurrent with the reset we happen to successfully reconnect.

We just deny initiating a reset if we are reconnecting.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>