[ddraw] Fix discrepancy in alpha mask for WINED3DFMT_B2G3R3A8_UNORM.

[Stefan Dösinger]

Am 02.05.2010 um 08:26 schrieb Vincent Pelletier:

> 
> PixelFormat_DD2WineD3D returns WINED3DFMT_B2G3R3A8_UNORM when alpha mask
> is 0xFF00, which is consistent with constant name (A8).
The patch looks ok to me.