nir-to-spirv: Cast SSBO input pointer when needed

Fixes validation error:

  VUID-VkShaderModuleCreateInfo-pCode-08737
  AtomicFAddEXT: expected Pointer to point to a value of type Result
Type
     %51 = OpAtomicFAddEXT %float %49 %uint_1 %uint_0 %50

when running

• spec@nv_shader_atomic_float@execution@ssbo-atomicadd-float

Fixes: 9f6be8effb43fcd4ce2fd00045bc6244ddf63529
    zink: store and use alu types for ntv defs