MINOR: samples: rename a struct from sample_storage to sample_data

This a first step of sample reorganization.
diff --git a/include/proto/pattern.h b/include/proto/pattern.h
index 7855474..0a132f2 100644
--- a/include/proto/pattern.h
+++ b/include/proto/pattern.h
@@ -208,7 +208,7 @@
 struct pattern_expr *pattern_lookup_expr(struct pattern_head *head, struct pat_ref *ref);
 struct pattern_expr *pattern_new_expr(struct pattern_head *head, struct pat_ref *ref,
                                       char **err, int *reuse);
-struct sample_storage **pattern_find_smp(struct pattern_expr *expr, struct pat_ref_elt *elt);
+struct sample_data **pattern_find_smp(struct pattern_expr *expr, struct pat_ref_elt *elt);
 int pattern_delete(struct pattern_expr *expr, struct pat_ref_elt *ref);