Since Linux Kernel commit 63706172f332 ("kthreads: rework
kthread_stop()"), made in 2009 in Linux Kernel v2.6.31-rc1, it has not
been necessary for kernel threads to call do_exit(). Since we do not
support kernels earlier than that, remove the call to
qdf_exit_thread(), the abstraction function for do_exit().
See Change-Id I22f27692fa8766df080630b9b0640c259285557c for more
information on why this call is being removed.
Change-Id: I4de812397e8910e5117bc142bf9185c02d2d3ec0
CRs-Fixed: 3300459
8b3dca1820