vt: perform safe console erase in the right order

vt: perform safe console erase in the right order

Commit 4b4ecd9cb853 ("vt: Perform safe console erase only once") removed
what appeared to be an extra call to scr_memsetw(). This missed the fact
that set_origin() must be called before clearing the screen otherwise
old screen content gets restored on the screen when using vgacon. Let's
fix that by moving all the scrollback handling to flush_scrollback()
where it logically belongs, and invoking it before the actual screen
clearing in csi_J(), making the code simpler in the end.

Reported-by: Matthew Whitehead <[email protected]>
Signed-off-by: Nicolas Pitre <[email protected]>
Tested-by: Matthew Whitehead <[email protected]>
Fixes: 4b4ecd9cb853 ("vt: Perform safe console erase only once")
Cc: [email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>