nvmet: configfs code cleanup

This is a pure code cleanup patch which does not change any
functionality. This patch removes the extra lines, get rid of
else which is duplicate for return.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>