EFCR register contains RS-485 configuration which should not
be changed by shutdown.  Instead of doing a write only update
the appropriate bits.
Signed-off-by: NJakub Kicinski <kubakici@wp.pl>
Signed-off-by: NJon Ringle <jringle@gridpoint.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>