i2c-bfin-twi: add a timeout to busbusy polling

Some faulty i2c slave devices might hold the sda/scl line and cause the
i2c bus driver to wait indefinitely in the busbusy loop.  Add a timeout
to the loop so the bus master can recover without locking up everything.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>