[IRDA]: stir4200 fixes.

From: Olaf Hartmann <olaf.hartmann@s1998.tu-chemnitz.de>

The attached patch observes the stir4200 fifo size and will clear the
fifo, if the size is increasing, while it should be transmitting bytes

Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>