drm/repaper: Reduce temporary buffer size in repaper_fb_dirty()

As the temporary buffer is no longer used to store 8-bit grayscale data,
its size can be reduced to the size needed to store the monochrome
bitmap data.

Fixes: 24c6bede ("drm/repaper: Use format helper for xrgb8888 to monochrome conversion")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220317081830.1211400-6-geert@linux-m68k.org

drivers/gpu/drm/tiny/repaper.c

@@ -533,7 +533,7 @@ static int repaper_fb_dirty(struct drm_framebuffer *fb)
 	DRM_DEBUG("Flushing [FB:%d] st=%ums\n", fb->base.id,
 		  epd->factored_stage_time);
 
-	buf = kmalloc_array(fb->width, fb->height, GFP_KERNEL);
+	buf = kmalloc(fb->width * fb->height / 8, GFP_KERNEL);
 	if (!buf) {
 		ret = -ENOMEM;
 		goto out_exit;