NVMe: Need to lock queue during interrupt handling

If we're sharing a queue between multiple CPUs and we cancel a sync I/O,
we must have the queue locked to avoid corrupting the stack of the thread
that submitted the I/O.  It turns out this is the same locking that's needed
for the threaded irq handler, so share that code.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>