nvme-core: put ctrl ref when module ref get fail

When try_module_get() fails in the nvme_dev_open() it returns without
releasing the ctrl reference which was taken earlier.

Put the ctrl reference which is taken before calling the
try_module_get() in the error return code path.

Fixes: 52a3974f "nvme-core: get/put ctrl and transport module in nvme_dev_open/release()"
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>