sunsab: Do not set sunsab_reg.cons right before registering minors.

Other Sun serial drivers do not do this, and if we keep it this way
it ends up registering all serial devices as consoles rather than
just the one which we explicitly register via sunserial_console_match()
which uses add_preferred_console().

Signed-off-by: David S. Miller <davem@davemloft.net>