nvmet: Fixed avoided printing nvmet: twice in error logs.

This patch avoids printing "nvmet:" twice in error logs as its already
coming through pr_fmt macro.

Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@fb.com>