urldata: include curl_sspi.h when Windows SSPI is enabled

f77dabe broke builds in Windows using Windows SSPI but not Windows SSL.

Bug: https://github.com/curl/curl/issues/1276
Reported-by: jveazey@users.noreply.github.com

lib/urldata.h

@@ -136,8 +136,10 @@
 #undef realloc
 #endif /* USE_AXTLS */
 
-#ifdef USE_SCHANNEL
+#if defined(USE_SCHANNEL) || defined(USE_WINDOWS_SSPI)
 #include "curl_sspi.h"
+#endif
+#ifdef USE_SCHANNEL
 #include <schnlsp.h>
 #include <schannel.h>
 #endif