wininet: Fix compiler warnings with flag -Wcast-qual.

dlls/wininet/urlcache.c

@@ -1175,8 +1175,8 @@ static inline HASH_CACHEFILE_ENTRY * URLCache_HashEntryFromOffset(LPCURLCACHE_HE
 static inline BOOL URLCache_IsHashEntryValid(LPCURLCACHE_HEADER pHeader, const HASH_CACHEFILE_ENTRY *pHashEntry)
 {
     /* check pHashEntry located within acceptable bounds in the URL cache mapping */
-    return ((DWORD)((LPBYTE)pHashEntry - (LPBYTE)pHeader) >= ENTRY_START_OFFSET) &&
-           ((DWORD)((LPBYTE)pHashEntry - (LPBYTE)pHeader) < pHeader->dwFileSize);
+    return ((DWORD)((const BYTE*)pHashEntry - (const BYTE*)pHeader) >= ENTRY_START_OFFSET) &&
+           ((DWORD)((const BYTE*)pHashEntry - (const BYTE*)pHeader) < pHeader->dwFileSize);
 }
 
 static BOOL URLCache_FindHash(LPCURLCACHE_HEADER pHeader, LPCSTR lpszUrl, struct _HASH_ENTRY ** ppHashEntry)