exiv2: add missing CVE tag to patch

Details: https://nvd.nist.gov/vuln/detail/CVE-2021-29458
https://nvd.nist.gov/vuln/detail/CVE-2021-31292

The patch is already present, but it was missing the CVE tag, which
is added in this change.

The same patch fixes both CVEs.

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>

meta-oe/recipes-support/exiv2/exiv2/CVE-2021-29458.patch

@@ -2,6 +2,9 @@ From 9b7a19f957af53304655ed1efe32253a1b11a8d0 Mon Sep 17 00:00:00 2001
 From: Kevin Backhouse <kevinbackhouse@github.com>
 Date: Fri, 9 Apr 2021 13:37:48 +0100
 Subject: [PATCH] Fix integer overflow.
+
+CVE: CVE-2021-29458 CVE-2021-31292
+
 ---
  src/crwimage_int.cpp | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)