Fix for a crash for the (fallow_cleaning && LRU_reclaim) case.

Summary: Fix for a copy-paste bug, which can cause crashes when fallow cleaning is enabled in
conjunction with LRU reclamation. Found by Vyacheslav Maslow and Wang Ning. This bug was also
fixed a long time ago (but not committed) by Kumar Sundararajan (facebook).

Test Plan:

Reviewers:

CC:

Task ID: #

Blame Rev:

src/flashcache_main.c

@@ -1170,7 +1170,7 @@ flashcache_clean_set(struct cache_c *dmc, int set)
 			cacheblk = &dmc->cache[lru_rel_index + start_index];
 			if ((cacheblk->cache_state & (DIRTY | BLOCK_IO_INPROG)) == DIRTY) {
 				cacheblk->cache_state |= DISKWRITEINPROG;
-				flashcache_clear_fallow(dmc, i);
+				flashcache_clear_fallow(dmc, lru_rel_index + start_index);
 				writes_list[nr_writes].dbn = cacheblk->dbn;
 				writes_list[nr_writes].index = cacheblk - &dmc->cache[0];
 				nr_writes++;