gallium/tgsi_to_nir: Set nir_intrinsic_align_mul to 1
Since the alignment is now checked in the validator we must set it.
TBH I'm not sure which alignment should be set, so I set it to 4, because that is what dest bitsize / 8 is, and in other places the alignment is set like this.
Fixes: e78a7a18 nir: Assert memory loads are aligned
@jekstrand