"Move" "common code" out to PTR_NOD, which does the conversion from private
pointer to node number.  This is to reduce potential casting/conversion errors
due to redundancy.  (The naming PTR_NOD follows PTR_ERR, turning a pointer
into xyz.)

[akpm@osdl.org: cleanups]
Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>