Bluetooth: Change fifo_fill to poll_out

The reason why fifo_fill works in qemu but not on real hardware is
that qemu serializes all byte transmission 1 by 1. There is no
real hardware fifo emulated, and "fifo" depth is 1. On real
hardware, the controller owns an internal fifo, with a depth like
8 bytes on Quark x1000. And because of execution flow, how fast is
the controller etc etc... a fifo_fill call might fill in the
internal fifo of 8 bytes and then controller says "I am full"
(which means: "wait for the fifo to have space again"). That's
why poll_out() works: it does the same as fifo_fill and wait
that the internal fifo gets some space again before continuing.
And only when all bytes have been pushed in, it returns.

Change-Id: I452a6ebb2913c5e52ed01d999185e250aa3ed474
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>