refspec.c: use designated initializers for "struct refspec_item"

Change the "struct refspec_item" at the top of refspec.c to use
designated initializers. Let's keep the "= 0" assignments for
self-documentation purposes, even though they're now redundant.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refspec.c

@@ -4,13 +4,13 @@
 #include "refspec.h"
 
 static struct refspec_item s_tag_refspec = {
-	0,
-	1,
-	0,
-	0,
-	0,
-	"refs/tags/*",
-	"refs/tags/*"
+	.force = 0,
+	.pattern = 1,
+	.matching = 0,
+	.exact_sha1 = 0,
+	.negative = 0,
+	.src = "refs/tags/*",
+	.dst = "refs/tags/*",
 };
 
 /* See TAG_REFSPEC for the string version */