gallium/tgsi_to_nir: Set nir_intrinsic_align_mul to 16 and offset to 0

gallium/tgsi_to_nir: Set nir_intrinsic_align_mul to 16 and offset to 0

Since the alignment is now checked in the validator we must set it.

v2: Use alignement of 4, i.e. dest bit size by eight.
v3: Use alignment 16 (Rhys Perry & Jason Ekstand)
v4: Use nir_intrinsic_set_align to make it clear that align offset is 0
    (Jason)

Fixes: e78a7a182524f091e2d77ba97bfbe057c3975cab
    nir: Assert memory loads are aligned

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4544>