ipc/mqueue: improve exception handling in do_mq_notify()

ipc/mqueue: improve exception handling in do_mq_notify()

Null pointers were assigned to local variables in a few cases as exception
handling.  The jump target “out” was used where no meaningful data
processing actions should eventually be performed by branches of an if
statement then.  Use an additional jump target for calling dev_kfree_skb()
directly.

Return also directly after error conditions were detected when no extra
clean-up is needed by this function implementation.

Link: http://lkml.kernel.org/r/592ef10e-0b69-72d0-9789-fc48f638fdfd@web.de
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>