ck_hs: Increase linear probe factor to twice what it was.

This assumes adjacent sector prefetch and appears to have minimal
clustering effect. In addition to this, developers are free to define
their own linear probe length by defining CK_HS_PROBE_L1_SHIFT.

src/ck_hs.c

@@ -35,7 +35,10 @@
 
 #include "ck_internal.h"
 
-#define CK_HS_PROBE_L1_SHIFT 3ULL
+#ifndef CK_HS_PROBE_L1_SHIFT
+#define CK_HS_PROBE_L1_SHIFT 4ULL
+#endif /* CK_HS_PROBE_L1_SHIFT */
+
 #define CK_HS_PROBE_L1 (1 << CK_HS_PROBE_L1_SHIFT)
 #define CK_HS_PROBE_L1_MASK (CK_HS_PROBE_L1 - 1)