As the matrix to be inverted is posdef the following (thanks to @carlobaldassi)
function inplaceinverse!(dest,source)
copy!(dest, source)
Base.LinAlg.inv!(cholfact!(dest))
end
suits my needs. Thanks to @stevengj for his suggestion but unfortunately I need the diagonal of the inverse of a posdef matrix. Maybe, but this is a question on linear algebra, there is a smarter strategy to obtain the diagonal of the inverse of a posdef matrix in a faster and less memory requiring way.