ipc,sem: open code and rename sem_lock

ipc,sem: open code and rename sem_lock

Rename sem_lock() to sem_obtain_lock(), so we can introduce a sem_lock()
later that only locks the sem_array and does nothing else.

Open code the locking from ipc_lock() in sem_obtain_lock() so we can
introduce finer grained locking for the sem_array in the next patch.

[[email protected]: propagate the ipc_obtain_object() errno out of sem_obtain_lock()]
Signed-off-by: Rik van Riel <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Cc: Chegu Vinod <[email protected]>
Cc: Emmanuel Benisty <[email protected]>
Cc: Jason Low <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Peter Hurley <[email protected]>
Cc: Stanislav Kinsbursky <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>