Input: at32psif - do not sleep in atomic context

We can't use msleep() while holding a spinlock, moreower serio's write()
method is supposed to be useable from inettrupt context. Let's do what
i8042 does and poll the status register every 50 us (with udelay).

Reported-by: Marjan Fojkar <marjan@pajkc.eu>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>