Fix mistaken use of CRYPTO_EX_INDEX_DSA in rsa.c.

Change-Id: I4a81fcbdd79f96b34cafcbd33279906b55dafbac
Reviewed-on: https://boringssl-review.googlesource.com/3920
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/rsa/rsa.c b/crypto/rsa/rsa.c
index 86fd2aa..691cd03 100644
--- a/crypto/rsa/rsa.c
+++ b/crypto/rsa/rsa.c
@@ -125,7 +125,7 @@
   }
   METHOD_unref(rsa->meth);
 
-  CRYPTO_free_ex_data(CRYPTO_EX_INDEX_DSA, rsa, &rsa->ex_data);
+  CRYPTO_free_ex_data(CRYPTO_EX_INDEX_RSA, rsa, &rsa->ex_data);
 
   if (rsa->n != NULL) {
     BN_clear_free(rsa->n);