ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()

ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()

After we acquire the sma->sem_perm lock in exit_sem(), we are protected
against a racing IPC_RMID operation.  Also at that point, we are the last
user of sem_undo_list.  Therefore it isn't required that we acquire or use
ulp->lock.

Signed-off-by: Herton R. Krzesinski <[email protected]>
Acked-by: Manfred Spraul <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Rafael Aquini <[email protected]>
CC: Aristeu Rozanski <[email protected]>
Cc: David Jeffery <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>