nir: Don't use ffma in nir_lower_wpos_ytransform().
nir: Don't use ffma in nir_lower_wpos_ytransform().

ffma is an explicitly fused multiply add with higher precision.
The optimizer will take care of promoting mul/add to fma when
it's beneficial to do so.

This fixes failures on Gen4-5 when using this pass, as those platforms
don't actually implement fma().

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler