Remove magic macros for screen_info structure members

Stop using magic macros for screen_info structure members.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/drivers/video/vga16fb.c b/drivers/video/vga16fb.c
index 2a14d28..9b3c592 100644
--- a/drivers/video/vga16fb.c
+++ b/drivers/video/vga16fb.c
@@ -1364,7 +1364,7 @@
 	par = info->par;
 
 	mutex_init(&par->open_lock);
-	par->isVGA = ORIG_VIDEO_ISVGA;
+	par->isVGA = screen_info.orig_video_isVGA;
 	par->palette_blanked = 0;
 	par->vesa_blanked = 0;