Fix 'ceil' is not defined

[dofuuz]

When using ResidualFSQ, this error occurs:

  File "(path removed)/lib/python3.12/site-packages/vector_quantize_pytorch/residual_fsq.py", line 32, in round_up_multiple
    return ceil(num / mult) * mult
           ^^^^
NameError: name 'ceil' is not defined

[lucidrains]

@dofuuz hey thanks!