r300g: Include missing header in r300_texture_desc.h.

Include p_format.h for enum pipe_format symbol.

Fixes r300g build.

src/gallium/drivers/r300/r300_texture_desc.h

@@ -24,6 +24,7 @@
 #ifndef R300_TEXTURE_DESC_H
 #define R300_TEXTURE_DESC_H
 
+#include "pipe/p_format.h"
 #include "r300_defines.h"
 
 struct pipe_resource;