Fix WOLFTPM2_USE_SW_ECDHE.

Author: dgarske

src/tpm2_cryptocb.c

@@ -180,11 +180,15 @@ int wolfTPM2_CryptoDevCb(int devId, wc_CryptoInfo* info, void* ctx)
             int curve_id;
             WOLFTPM2_KEY* key;
 
+        #ifdef WOLFTPM2_USE_SW_ECDHE
+            if (tlsCtx->ecdhKey == NULL) {
+                return exit_rc;
+            }
+        #endif
+
             if (   tlsCtx->eccKey   == NULL
                 && tlsCtx->ecdsaKey == NULL
-            #ifndef WOLFTPM2_USE_SW_ECDHE
                 && tlsCtx->ecdhKey  == NULL
-            #endif
             ) {
             #ifdef DEBUG_WOLFTPM
                 printf("No crypto callback key pointer set!\n");

wolftpm/tpm2_wrap.h

@@ -3347,9 +3347,7 @@ typedef struct TpmCryptoDevCtx {
 #ifdef HAVE_ECC
     WOLFTPM2_KEY* eccKey;       /* ECDSA - public only */
     WOLFTPM2_KEYBLOB* ecdsaKey; /* ECDSA - retain encrypted private portion from keygen */
-    #ifndef WOLFTPM2_USE_SW_ECDHE
     WOLFTPM2_KEY* ecdhKey;      /* ECDH */
-    #endif
 #endif
     WOLFTPM2_KEY* storageKey;
 #ifdef WOLFTPM_USE_SYMMETRIC