d3d9: Set RGBA4 to unknown

Color ordering of RGBA4 is wrong and there are no A4B4G4A4 format or swizzling
options.

src/renderer_d3d9.cpp

@@ -235,7 +235,7 @@ namespace bgfx { namespace d3d9
 		{ D3DFMT_UNKNOWN       }, // RGBA32U
 		{ D3DFMT_A32B32G32R32F }, // RGBA32F
 		{ D3DFMT_R5G6B5        }, // R5G6B5
-		{ D3DFMT_A4R4G4B4      }, // RGBA4
+		{ D3DFMT_UNKNOWN       }, // RGBA4
 		{ D3DFMT_A1R5G5B5      }, // RGB5A1
 		{ D3DFMT_A2B10G10R10   }, // RGB10A2
 		{ D3DFMT_UNKNOWN       }, // RG11B10F