Input: i8042 - fix locking in interrupt routine

We need to protect not only i8042 status and data register from concurrent
access from IRQ 1 and 12 but the rest of the shared state as well, so let's
move release of i8042_lock in i8042_interrupt() a little bit further down.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>