Annotate some functions to prevent Coverity tainted input error.

These errors are really annoying, just silence them.

lib/random.c

@@ -171,6 +171,7 @@ err:
 	return -ENOSYS;
 }
 
+/* coverity[ -taint_source : arg-1 ] */
 int crypt_random_get(struct crypt_device *ctx, char *buf, size_t len, int quality)
 {
 	int status, rng_type;