What do you want to do with them after? What do you want to happen to the bits left over when the length isn't divisible by 128?
You can just create a vector of start indices for each, e.g.
idx = cellfun( @(x) 1:128:numel(x), 'UniformOutput', false );
and then use those for future operations into the segments. Or to put them each into their own cell of a new cell array if you really want. Or, if you are going to discard any segments less than 128 length you can put them into a 128 x n matrix, n being however many segments you end up with.
