LU-8802 obd: str2dev is missing obd_device_unlock()

LU-8802 obd: str2dev is missing obd_device_unlock()

class_str2dev() was missing an obd_device_unlock(). I haven't
seen any bugs related to this missing unlock. I suspect
the mount state machine avoids this. Add the unlock just
to be safe.

Fixes: c5e5060d950 ("LU-8802 obd: remove MAX_OBD_DEVICES")
Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I7a813f9d4931a7a9979223bfde5efea07f1e5228
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53466
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>