util/ar: Fix integer conversion in bounds check

Some code scanner was complaining.

Change-Id: I371aa5fb4519a5a938f452e06b61941cd674848e
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/96647
Reviewed-by: Lily Chen <chlily@google.com>
Commit-Queue: Lily Chen <chlily@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
Presubmit-BoringSSL-Verified: boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>

util/ar/ar.go

diff --git a/util/ar/ar.go b/util/ar/ar.go
index 709b158..a06b065 100644
--- a/util/ar/ar.go
+++ b/util/ar/ar.go
@@ -101,7 +101,7 @@
 				return nil, errors.New("ar: filename offset overflow")
 			}
 
-			if int(offset) > len(longFilenameTable) {
+			if offset > uint64(len(longFilenameTable)) {
 				return nil, errors.New("ar: filename offset out of bounds")
 			}