Input: bcm5974 - switch back to normal mode when closing

Staying in multi-touch mode after closing the device sometimes makes
the keyboard drop keys or repeat keys irratically. The conjecture is
that some internal buffer starts to overflow, resulting in undefined
behavior. Switching back to normal mode when closing the device makes
the problem go away.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>