Revert "kbuild: specify absolute paths for cscope"

This reverts commit eb8f844c. Ian
Campbell writes:
> I keep my kernel source tree on a more powerful build box where I run my
> builds etc (including "make cscope") but run my editor from my
> workstation with an NFS mount to the source. This worked fine for me
> using relative paths for cscope. Using absolute paths in cscope breaks
> this previously working setup because the root path is not the same on
> both systems. I guess this is similar to moving the source tree around.
>
> Without wanting to start a flamewar it really sounds to me like we are
> working around a vim (or cscope) bug here, emacs with cscope bindings
> works fine in this configuration.

Given that absolute paths can be forced by make O=. cscope, change the
default back to relative paths.

Ian Campbell <ijc@hellion.org.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Michal Marek <mmarek@suse.cz>