Because of the change introduced in
f21693b2 vkd3d-shader/hlsl: Use reg_size as component count when allocating a single register.
SM1 scalars and vectors were not longer getting the correct writemask
when they are allocated.
This happened because they have to reserve the whole register even if
they only use some of its components, so their reg_size may differ from
the number of components.
This commit fixes that.