Input: walkera0701 - fix crash on startup

The driver's timer must be set up before enabling IRQ handler, otherwise
bad things may happen.

Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Peter Popovec <popovec@fei.tuke.sk>
CC: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>