CVE-2023-52731

In the Linux kernel, the following vulnerability has been resolved:

fbdev: Fix invalid page access after closing deferred I/O devices

When a fbdev with deferred I/O is once opened and closed, the dirty
pages still remain queued in the pageref list, and eventually later
those may be processed in the delayed work. This may lead to a
corruption of pages, hitting an Oops.

This patch makes sure to cancel the delayed work and clean up the
pageref list at closing the device for addressing the bug. A part of
the cleanup code is factored out as a new helper function that is
called from the common fb_release().