Right now two copy up helpers are in inode.c.  Amir suggested it might be
better to move these to copy_up.c.

There will one more related function which will come in later patch.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>