The corrcoef function cannot accept histogram object handles. You may have better luck using corrcoef on the vectors of bin counts from two calls to histcounts (using the same set of edges for each call) instead.
% Sample data
x1 = randn(1, 1e5);
x2 = 2*randn(1, 1e5);
% Obtain the vectors of bin counts. Use the set of edges returned from the first call
% as an input to the second call so the vector of bin counts are the same length and
% measure "apples to apples"
[n2, edges] = histcounts(x2);
n1 = histcounts(x1, edges);
% Compute the correlation coefficient between the vectors of bin counts
corrcoef(n1, n2)
