keygen test not generating the key for every iteration

key_transform field not being reset during DeleteKey() causing
keygen test to skip the key generation.

Bug: 375151780
Test: VtsAidlKeyMintBenchmarkTest
Change-Id: I10428dc9f84831a44917fb180d16bb97e2db2257
diff --git a/security/keymint/aidl/vts/performance/KeyMintBenchmark.cpp b/security/keymint/aidl/vts/performance/KeyMintBenchmark.cpp
index 49fd0c9..781b7a6 100644
--- a/security/keymint/aidl/vts/performance/KeyMintBenchmark.cpp
+++ b/security/keymint/aidl/vts/performance/KeyMintBenchmark.cpp
@@ -294,6 +294,7 @@
     ErrorCode DeleteKey() {
         Status result = keymint_->deleteKey(key_blob_);
         key_blob_ = vector<uint8_t>();
+        key_transform_ = "";
         return GetReturnErrorCode(result);
     }