Blackfin arch: Fix bug - BF518 port F, G, and H have different mux offset compare to BF527

[Mike Frysinger <vapier.adi@gmail.com>: keep the ifdef nest down]

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>