FS-Cache: Add a retirement stat counter

Add a stat counter to count retirement events rather than ordinary release
events (the retire argument to fscache_relinquish_cookie()).

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index f979659..9905350 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -415,6 +415,8 @@
 	unsigned long event;
 
 	fscache_stat(&fscache_n_relinquishes);
+	if (retire)
+		fscache_stat(&fscache_n_relinquishes_retire);
 
 	if (!cookie) {
 		fscache_stat(&fscache_n_relinquishes_null);