Ensure that "out" is initialized in all error paths.

Reported by:	gcc
Reviewed by:	cem
Differential Revision:	https://reviews.freebsd.org/D13402

lib/libefivar/efivar-dp-xlate.c

@@ -529,7 +529,7 @@ build_dp(const char *efimedia, const char *relpath, efidp *dp)
 {
 	char *fp, *dptxt = NULL;
 	int rv = 0;
-	efidp out;
+	efidp out = NULL;
 	size_t len;
 
 	fp = path_to_file_dp(relpath);