add intents in abstract interface func of newuoa_module

[Beliavsky]

I suggest that the abstract interface look as follows:

    abstract interface
    subroutine func (n, x, f)  !! calfun interface
        import :: wp
        implicit none
        integer  , intent(in)  :: n
        real (wp), intent(in)  :: x (*)
        real (wp), intent(out) :: f
    end subroutine func
    end interface