debugfs: switch to simple_follow_link()

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/debugfs/file.c
Simple merge

diff --cc fs/debugfs/inode.c
Simple merge

diff --cc include/linux/debugfs.h
Simple merge