MINOR: sample: dont call the sample cast function "c_none"

If the cast function to execute is c_none, dont execute it and return
true. The function c_none, do nothing. This save a call.
diff --git a/src/sample.c b/src/sample.c
index f57811e..7568d27 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -559,7 +559,7 @@
 }
 
 
-static int c_none(struct sample *smp)
+int c_none(struct sample *smp)
 {
 	return 1;
 }