nvmet/fcloop: remove some logically dead code performing redundant ret checks

The check to see if ret is non-zero and return this rather than count
is redundant in two occassions.  It is redundant because prior to this
check, the return code ret is already checked for a non-zero error
return value and we return from the function at that point.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>