Move deref to after non-null assert

Asserting afterwards triggers a GCC static analysis error:

source/sigv4.c:2413:5: warning: check of ‘pHmacContext_22(D)’ for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
 2413 |     assert( pHmacContext != NULL );
      |     ^
  ‘hmacIntermediate’: events 1-2
    |
    | 2411 |     const SigV4CryptoInterface_t * pCryptoInterface = pHmacContext->pCryptoInterface;
    |      |                                    ^
    |      |                                    |
    |      |                                    (1) pointer ‘pHmacContext_22(D)’ is dereferenced here
    | 2412 |
    | 2413 |     assert( pHmacContext != NULL );
    |      |     ~
    |      |     |
    |      |     (2) pointer ‘pHmacContext_22(D)’ is checked for NULL here but it was already dereferenced at (1)
    |

Author: archigup

source/sigv4.c

@@ -2408,7 +2408,7 @@ static int32_t hmacIntermediate( HmacContext_t * pHmacContext,
 {
     int32_t returnStatus = 0;
     size_t i = 0U;
-    const SigV4CryptoInterface_t * pCryptoInterface = pHmacContext->pCryptoInterface;
+    const SigV4CryptoInterface_t * pCryptoInterface;
 
     assert( pHmacContext != NULL );
     assert( dataLen > 0U );
@@ -2417,7 +2417,9 @@ static int32_t hmacIntermediate( HmacContext_t * pHmacContext,
     assert( pHmacContext->pCryptoInterface->hashInit != NULL );
     assert( pHmacContext->pCryptoInterface->hashUpdate != NULL );
     assert( pHmacContext->pCryptoInterface->hashFinal != NULL );
-    assert( pHmacContext->keyLen == pCryptoInterface->hashBlockLen );
+    assert( pHmacContext->keyLen == pHmacContext->pCryptoInterface->hashBlockLen );
+
+    pCryptoInterface = pHmacContext->pCryptoInterface;
 
     /* Derive the inner HMAC key by XORing the key with inner pad byte. */
     for( i = 0U; i < pCryptoInterface->hashBlockLen; i++ )