[ Upstream commit 9e6aea22802b5684c7e1d69822aeb0844dd01953 ]

Included file path was hard-wired in the ocfs2 makefile, which might
causes some confusion when compiling ocfs2 as an external module.

Say if we compile ocfs2 module as following.
cp -r /kernel/tree/fs/ocfs2 /other/dir/ocfs2
cd /other/dir/ocfs2
make -C /path/to/kernel_source M=`pwd` modules

Acutally, the compiler wil try to find included file in
/kernel/tree/fs/ocfs2, rather than the directory /other/dir/ocfs2.

To fix this little bug, we introduce the var $(src) provided by kbuild.
$(src) means the absolute path of the running kbuild file.

Link: http://lkml.kernel.org/r/20181108085546.15149-1-lchen@suse.com
Signed-off-by: Larry Chen
Reviewed-by: Andrew Morton
Cc: Mark Fasheh
Cc: Joel Becker
Cc: Junxiao Bi
Cc: Joseph Qi
Cc: Changwei Ge
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
Signed-off-by: Sasha Levin