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)" <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Tested-by: Helge Deller <[e-mail]> # parisc STI console
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/vt/vt.c

···
 	if (entering_gfx) {
 		hide_cursor(vc);
 		save_screen(vc);
-		vc->vc_sw->con_blank(vc, -1, 1);
+		vc->vc_sw->con_blank(vc, 1, 1);
 		console_blanked = fg_console + 1;
 		blank_state = blank_off;
 		set_origin(vc);

drivers/video/console/vgacon.c

···
 		/* Tell console.c that it has to restore the screen itself */
 		return 1;
 	case 1:		/* Normal blanking */
-	case -1:	/* Obsolete */
 		if (!mode_switch && vga_video_type == VIDEO_TYPE_VGAC) {
 			vga_pal_blank(&vgastate);
 			vga_palette_blanked = true;