When using a separate output directory the in-kernel config wiere rebuild
each time the kernel was compiled.  Fix this by specifying correct path to
Makefile in the prerequisite to the ikconfig.h file.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>