Fix for issues #988 and #997

This patch fixes the issue 988 (and 997) causing a kernel stack
overflow.

Signed-off-by: Krzysztof Majzerowicz-Jaszcz <krzysztof.majzerowicz-jaszcz@intel.com>

src/engine/engine_pt.c

@@ -121,7 +121,7 @@ int ocf_read_pt(struct ocf_request *req)
 	ocf_engine_traverse(req);
 
 	if (req->seq_cutoff && ocf_engine_is_dirty_all(req) &&
-			!req->bf_blocked) {
+			!req->force_pt) {
 		use_cache = true;
 	} else {
 		if (ocf_engine_mapped_count(req)) {