Blackfin: update handling of anomaly 364 (wrong rev id in BF527-0.1)

This anomaly only applies to the BF527-0.1, not the BF526-0.1, and not any
other revision of the BF527.  So make sure we don't go returning 0xffff
for other cases.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>