Blackfin: spi: there is no PORTJ_FER MMR on BF537

Since the PORTJ on the BF537 is peripheral-only (no GPIO functionality),
then there is no PORTJ_FER register for us to worry about.

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