qxl: avoid an oops in the deferred io code.

If we are using deferred io due to plymouth or X.org fbdev driver
we will oops in memcpy due to this pointless multiply here,

removing it fixes fbdev to start and not oops.

Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/qxl/qxl_fb.c

@@ -108,7 +108,7 @@ static void qxl_fb_dirty_flush(struct fb_info *info)
 	u32 x1, x2, y1, y2;
 
 	/* TODO: hard coding 32 bpp */
-	int stride = qfbdev->qfb.base.pitches[0] * 4;
+	int stride = qfbdev->qfb.base.pitches[0];
 
 	x1 = qfbdev->dirty.x1;
 	x2 = qfbdev->dirty.x2;