vkd3d-shader/msl: Get rid of a stray vkd3d_string_buffer_printf() in the VEC4 UINT immediate constant handling.
Uncovered by the ininf() test in the next commit. This is why we insist
on test coverage; unfortunately this one slipped through in
fd1beedc07becc7e5e49b64273f7bde7f9a8b2a0.