nvme-fcloop: fix inconsistent lock state warnings

With extra debug on, inconsistent lock state warnings are being called
out as the tfcp_req->reqlock is being taken out without irq, while some
calling sequences have the sequence in a softirq state.

Change the lock taking/release to raise/drop irq.

Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>