[PATCH] respect srctree/objtree in Documentation/DocBook/Makefile

The KERNELDOC and DOCPROC variables are relative to the
$(srctree)/$(objtree) and expect to be run only from there ...  attached
patch adds proper srctree/objtree prefixes to both variables.

Acked-by: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>