Avoid stack overflow when pending read misses list is blocked

Signed-off-by: Robert Baldyga <robert.baldyga@intel.com>

src/ocf_request.h

@@ -185,6 +185,9 @@ struct ocf_request {
 	uint8_t seq_cutoff : 1;
 	/*!< Sequential cut off set for this request */
 
+	uint8_t bf_blocked : 1;
+	/*!< Backfill pending read misses list blocked */
+
 	uint8_t wi_second_pass : 1;
 	/*!< Set after first pass of WI write is completed */