Input: i8042 - fix device removal on unload

We need to call platform_device_unregister(i8042_platform_device)
before calling platform_driver_unregister() because i8042_remove()
resets i8042_platform_device to NULL. This leaves the platform device
instance behind and prevents driver reload.

Fixes https://bugzilla.kernel.org/show_bug.cgi?id=16613



Reported-by: Seryodkin Victor <vvscore@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>