nvmet: remove unnecessary ctrl parameter

nvmet: remove unnecessary ctrl parameter

The function nvmet_ctrl_find_get() accepts out pointer to nvmet_ctrl
structure. This function returns the same error value from two places
that is :- NVME_SC_CONNECT_INVALID_PARAM | NVME_SC_DNR.

Move this to the caller so we can change the return type to nvmet_ctrl.

Now that we can changed the return type, instead of taking out pointer
to the nvmet_ctrl structure remove that function parameter and return
the valid nvmet_ctrl pointer on success and NULL on failure.

Also, add and rename the goto labels for more readability with comments.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>