BUILD: vars: avoid overlapping field initialization

Compiling vars.c with gcc 4.2 shows that we're initializing some local
structs field members in a not really portable way:

src/vars.c: In function 'vars_parse_cli_set_var':
src/vars.c:1195: warning: initialized field overwritten
src/vars.c:1195: warning: (near initialization for 'px.conf.args')
src/vars.c:1195: warning: initialized field overwritten
src/vars.c:1195: warning: (near initialization for 'px.conf')
src/vars.c:1201: warning: initialized field overwritten
src/vars.c:1201: warning: (near initialization for 'rule.conf')

It's totally harmless anyway, but better clean this up.
diff --git a/src/vars.c b/src/vars.c
index 4726786..4ed3a1d 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -1071,14 +1071,12 @@
 {
 	struct proxy px = {
 		.id = "CFG",
-		.conf.args.file = file,
-		.conf.args.line = line,
+		.conf.args = { .file = file, .line = line, },
 	};
 	struct act_rule rule = {
 		.arg.vars.scope = SCOPE_PROC,
 		.from = ACT_F_CFG_PARSER,
-		.conf.file = (char *)file,
-		.conf.line = line,
+		.conf = { .file = (char *)file, .line = line, },
 	};
 	enum obj_type objt = OBJ_TYPE_NONE;
 	struct session *sess = NULL;
@@ -1192,14 +1190,12 @@
 {
 	struct proxy px = {
 		.id = "CLI",
-		.conf.args.file = "CLI",
-		.conf.args.line = 0,
+		.conf.args = { .file = "CLI", .line = 0, },
 	};
 	struct act_rule rule = {
 		.arg.vars.scope = SCOPE_PROC,
 		.from = ACT_F_CLI_PARSER,
-		.conf.file = "CLI",
-		.conf.line = 0,
+		.conf = { .file = "CLI", .line = 0, },
 	};
 	enum obj_type objt = OBJ_TYPE_NONE;
 	struct session *sess = NULL;