Add missing lookup in engine_map()

Early return from engine_map() in case of insufficient free
cachelines on the freelist is opportunistic, as both request
map info and freelist count are not accurate. Map info is stale
as it is to be refreshed in engine_map() after hash bucket
lock had been upgraded. Freelist count on other hand is subject
to change asynchronously.

The implementation assumption however is that after engine_map()
request is fully traversed (engine_map() is equivalent to
engine_lookup() followed by an attempt to map missing cachelines).
So in case of early return we must take care of repeating the
lookup.

Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>

src/engine/engine_common.c

@@ -404,6 +404,7 @@ static void ocf_engine_map(struct ocf_request *req)
 
 	if (ocf_engine_unmapped_count(req) >
 			ocf_freelist_num_free(cache->freelist)) {
+		ocf_engine_lookup(req);
 		ocf_req_set_mapping_error(req);
 		return;
 	}