f2fs: init_dent_inode() should take qstr

for one thing, it doesn't (and shouldn't) use anything else from dentry;
for another, on some call chains the dentry is fake and should
be eliminated completely.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/f2fs/dir.c
Simple merge

diff --cc fs/f2fs/f2fs.h
Simple merge

diff --cc fs/f2fs/node.c
Simple merge