tty: vt: stop using -1 for blank mode in consw::con_blank()

tty: vt: stop using -1 for blank mode in consw::con_blank()

-1 is the same as VESA_VSYNC_SUSPEND in all con_blank() implementations.
So we can remove this special case from vgacon now too.

Despite con_blank() of fbcon looks complicated, the "if
(!fbcon_is_inactive(vc, info))" branch is not taken as we set
"ops->graphics = 1;" few lines above. So what matters there (as in all
other blank implementations except vgacon) is if 'blank' is zero or not.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Tested-by: Helge Deller <deller@gmx.de> # parisc STI console
Link: https://lore.kernel.org/r/20240122110401.7289-32-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>