net: atm: Convert timers to use timer_setup()

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new timer_setup() and from_timer()
to pass the timer pointer explicitly. Also drops a redundant initialization
that is already set up by DEFINE_TIMER.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Hans Liljestrand <ishkamiel@gmail.com>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Bhumika Goyal <bhumirks@gmail.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Cc: Augusto Mecking Caringi <augustocaringi@gmail.com>
Cc: Jarod Wilson <jarod@redhat.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>