Kobo Aura H2O: fix bezel.

The Kobo Aura H2O has only 1430x1080 visible pixels. The top 10 pixels are unfortunately hidden by the bezel. This commit makes KOReader display as intended.

A few general remarks:

* `getSizePhoenix` should probably be renamed to something more generic like `getSizeHardcoded` for clarity.
* I wrote `if Screen.cur_rotation_mode == 0 or Screen.cur_rotation_mode == 3` only because that's equivalent to the Phoenix code I modified. I saw no GUI way to get more than 2 types of rotation, so rotation_mode 3 remains untested.
* Surprisingly, no offSetY was required to obtain a correct display. On the contrary, adding it messed things up.
* The code would suggest that line 127 needs to be replaced by `if (self.device:getModel() == 'Kobo_phoenix' or self.device:getModel() == 'Kobo_dahlia') and refresh_type == 1 then` but I could only spot any differences with a few ghost lines while I was testing. Once I was done testing all possible offset values so they were correct, it seemed to make no difference one way or the other. That is, there were no odd artifacts on the screen when I left it out, so I left it out.