Prevent memory leak on error.

data.c

 	char tmp[9];
 	unsigned i, pos;
 
-	NIT *n = calloc(1, sizeof(NIT));
 	if (strlen(freq) != 9 || strlen(symbol_rate) != 8)
 		return NULL;
+	NIT *n = calloc(1, sizeof(NIT));
 	n->freq        = strdup(freq);
 	n->modulation  = strdup(mod);
 	n->symbol_rate = strdup(symbol_rate);