fbdev: Remove unused struct fb_deferred_io .first_io field

This optional callback was added in the commit 1f45f9dbb3 ("fb_defio:
add first_io callback") but it was never used by a driver. Let's remove
it since it's unlikely that will be used after a decade that was added.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230121192418.2814955-2-javierm@redhat.com

drivers/video/fbdev/core/fb_defio.c

@@ -157,10 +157,6 @@ static vm_fault_t fb_deferred_io_track_page(struct fb_info *info, unsigned long
 	/* protect against the workqueue changing the page list */
 	mutex_lock(&fbdefio->lock);
 
-	/* first write in this cycle, notify the driver */
-	if (fbdefio->first_io && list_empty(&fbdefio->pagereflist))
-		fbdefio->first_io(info);
-
 	pageref = fb_deferred_io_pageref_get(info, offset, page);
 	if (WARN_ON_ONCE(!pageref)) {
 		ret = VM_FAULT_OOM;

include/linux/fb.h

@@ -215,7 +215,6 @@ struct fb_deferred_io {
 	struct mutex lock; /* mutex that protects the pageref list */
 	struct list_head pagereflist; /* list of pagerefs for touched pages */
 	/* callback */
-	void (*first_io)(struct fb_info *info);
 	void (*deferred_io)(struct fb_info *info, struct list_head *pagelist);
 };
 #endif