fold try_to_ascend() into the sole remaining caller

fold try_to_ascend() into the sole remaining caller

commit 31dec1327e377b6d91a8a6c92b5cd8513939a233 upstream.

There used to be a bunch of tree-walkers in dcache.c, all alike.
try_to_ascend() had been introduced to abstract a piece of logics
duplicated in all of them.  These days all these tree-walkers are
implemented via the same iterator (d_walk()), which is the only
remaining caller of try_to_ascend(), so let's fold it back...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>