libertas: 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.

Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andrew Zaborowski <andrew.zaborowski@intel.com>
Cc: libertas-dev@lists.infradead.org
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>