ck_internal: Fix bsf behavior.

src/ck_internal.h

@@ -84,15 +84,19 @@ ck_internal_max_32(uint32_t x, uint32_t y)
 CK_CC_INLINE static unsigned long
 ck_internal_bsf(unsigned long v)
 {
+#if defined(__GNUC__)
+	return __builtin_ffs(v);
+#else
 	unsigned int i;
 	const unsigned int s = sizeof(unsigned long) * 8 - 1;
 
 	for (i = 0; i < s; i++) {
 		if (v & (1UL << (s - i)))
-			return i;
+			return sizeof(unsigned long) * 8 - i;
 	}
 
 	return 1;
+#endif /* !__GNUC__ */
 }
 
 CK_CC_INLINE static uint64_t