[media] nuvoton-cir: fix clearing wake fifo

[media] nuvoton-cir: fix clearing wake fifo

At least on NVT6779D clearing the wake fifo works in learning mode only
(although this condition is not mentioned in the chip spec).
Setting the clear fifo bit has no effect in wake up mode.
Even if clearing the wake fifo should work in wake up mode on other
chips this workaround doesn't hurt.
If needed the caller of nvt_clear_cir_wake_fifo has to take care
of locking.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>