nvme: remove single trailing whitespace

There is a single trailing whitespace in core.c.
Since this is just a single whitespace, the chances of this affecting
backports to stable should be quite low, so let's just remove it.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>