Assign the magic number to a macro

Signed-off-by: Austin Yuan <shengquan.yuan@intel.com>

src/va.c

@@ -58,7 +58,7 @@ static int va_debug_trace = 0;
 static int vaDisplayIsValid(VADisplay dpy)
 {
   VADisplayContextP pDisplayContext = (VADisplayContextP)dpy;
-  return pDisplayContext && (pDisplayContext->vadpy_magic == 0x789abcde) && pDisplayContext->vaIsValid(pDisplayContext);
+  return pDisplayContext && (pDisplayContext->vadpy_magic == VA_DISPLAY_MAGIC) && pDisplayContext->vaIsValid(pDisplayContext);
 }
 
 static void va_errorMessage(const char *msg, ...)

src/va_backend.h

@@ -396,6 +396,7 @@ struct VADriverContext
     void *dri_state;
 };
 
+#define VA_DISPLAY_MAGIC 0x56414430 /* VAD0 */
 struct VADisplayContext
 {
     int vadpy_magic;

src/x11/va_x11.c

@@ -189,7 +189,7 @@ VADisplay vaGetDisplay (
       dri_state       = calloc(1, sizeof(*dri_state));
       if (pDisplayContext && pDriverContext && dri_state)
       {
-	  pDisplayContext->vadpy_magic = 0x789abcde;          
+	  pDisplayContext->vadpy_magic = VA_DISPLAY_MAGIC;          
 
 	  pDriverContext->x11_dpy          = native_dpy;
 	  pDisplayContext->pNext           = pDisplayContexts;