cbus: handle possible errors on cbus_send/receive_bit

gpio_direction_input might fail and we have
to handle that possibility. While at that,
also add the device pointer to struct cbus_host
and use that for printing debugging messages and
make cbus_receive_bit return int.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>

diff --cc drivers/cbus/cbus.c
Simple merge