nvmet: initialize discovery subsys after debugfs is initialized

[ Upstream commit 52858994 ]

During nvme target initialization discovery subsystem is initialized
before "nvmet" debugfs directory is created. This results in discovery
subsystem debugfs directory to be created in debugfs root directory.

nvmet_init() ->
  nvmet_init_discovery() ->
    nvmet_subsys_alloc() ->
      nvmet_debugfs_subsys_setup()

In other words, the codepath above is exeucted before nvmet_debugfs is
created. We get /sys/kernel/debug/nqn.2014-08.org.nvmexpress.discovery
instead of /sys/kernel/debug/nvmet/nqn.2014-08.org.nvmexpress.discovery.
Move nvmet_init_discovery() call after nvmet_init_debugfs() to fix it.

Fixes: 649fd414 ("nvmet: add debugfs support")
Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>