Patch from Dipankar Sarma <dipankar@in.ibm.com>

All fs should be using dcache APIs to manipulate dcache hash lists.  This is
in line with the dcache cleanup patch (dcache_rcu-1) from Maneesh that Linus
accepted.  This seems like a reasonable cleanup.  One change though, we don't
need to grab dcache_lock while deleting dentries from the private list and
__d_drop() should suffice here.