inject_hash: Switch a bytes.Index to bytes.Contains

My editor was complaining that this should be simplified.

Change-Id: I221c50e27fc7a0bc943c044531ddcef95444f033
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/86087
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

util/fipstools/inject_hash/inject_hash.go

diff --git a/util/fipstools/inject_hash/inject_hash.go b/util/fipstools/inject_hash/inject_hash.go
index a06ce8b..a60a0e0 100644
--- a/util/fipstools/inject_hash/inject_hash.go
+++ b/util/fipstools/inject_hash/inject_hash.go
@@ -248,7 +248,7 @@
 		return errors.New("did not find uninitialised hash value in object file")
 	}
 
-	if bytes.Index(objectBytes[offset+1:], fipscommon.UninitHashValue[:]) >= 0 {
+	if bytes.Contains(objectBytes[offset+1:], fipscommon.UninitHashValue[:]) {
 		return errors.New("found two occurrences of uninitialised hash value in object file")
 	}