Blackfin: work around anomaly 05000189

Similar to anomaly 05000281 but not as bad, we cannot return to the
instruction causing a fault otherwise we'll trigger a second false
exception.  The system can still recover, but it isn't correct.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>