We already call nir_rematerialize_derefs_in_use_blocks_impl prior to
calling nir_lower_ssa_defs_to_regs_block so the assertion that all deref
uses in the block should hold. This fixes the following CTS test when
SPIR-V optimization recipe 1:
dEQP-VK.glsl.struct.local.loop_nested_struct_array_vertex
Fixes: 606eb56ab9 "intel/nir: Only lower load/store derefs"
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>