ipc/shm: do not use ipc_rcu_free()

ipc/shm: do not use ipc_rcu_free()

Avoid using ipc_rcu_free, since it just re-finds the original structure
pointer.  For the pre-list-init failure path, there is no RCU needed,
since it was just allocated.  It can be directly freed.

Link: http://lkml.kernel.org/r/20170525185107.12869-7-manfred@colorfullife.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>