net: wwan: iosm: drop debugfs dev reference

Post debugfs use call wwan_put_debugfs_dir()to drop
debugfs dev reference.

Signed-off-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: wwan: iosm: move debugfs knobs into a subdir

The modem traces collection is a device (and so driver) specific option.
Therefore, move the related debugfs files into a driver-specific
subdirectory under the common per WWAN device directory.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Acked-by: M Chetan Kumar <m.chetan.kumar@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>