[3/5] WineD3D: Fix D3DFMT_R32F, R16F, G16R16F, ... in the pixel shader

[Henri Verbeet]

I forgot to mention this in my previous mail, but if we're going to
change the color fixup code, we should really integrate it properly
into the backend. Ie, shader_glsl_get_sample_function() and the ARB
equivalent should be aware of the format conversion, in order to
prevent having to swizzle from components that aren't available, like
can happen with WINED3DFMT_L6V5U5.