ACER: Fix Smatch double-free issue

The patch 6ae3a0876185: "ACER: Add support for accelerometer sensor"
from Jun 1, 2012, leads to the following Smatch warning:
drivers/platform/x86/acer-wmi.c:1886 acer_wmi_accel_destroy()
         error: don't call input_free_device() after input_unregister_device()

drivers/platform/x86/acer-wmi.c
  1883  static void acer_wmi_accel_destroy(void)
  1884  {
  1885          input_unregister_device(acer_wmi_accel_dev);
  1886          input_free_device(acer_wmi_accel_dev);
  1887  }

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Fengguang Wu <wfg@linux.intel.com>
Cc: joeyli <jlee@suse.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>