LU-8066 obd_type: discard obd_type_lock

LU-8066 obd_type: discard obd_type_lock

This lock is only used to protect typ_refcnt, so change
that to an atomic_t and discard the lock.

The lock also covers calls to try_module_get and module_put,
but this serves no purpose as it does not prevent the module
from being unloaded.

Finally, the return value for the call to try_module_get is
ignored, which is not safe.

Linux-commit: 493ae16ed39a1c9f792c3b650e2dff11ca2e73e8

Change-Id: I904c51cc4d3426ca520c0bcad9665380ce1f3c3d
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-on: https://review.whamcloud.com/35096
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>