From: Maneesh Soni <maneesh@in.ibm.com>

This patch the corrects the dentry_stat.nr_unused calculation.

In select_parent() and shrink_dcache_anon() we were not doing any adjustments
to the nr_unused count after manipulating the dentry_unused list.  Now the
nr_unused count is decremented if the dentry is on dentry_unused list and is
removed from there.

Further in the same routines, we have to adjust the nr_unused count again if
the dentry is moved to the end of d_lru list for pruning.