serial: bfin_sport_uart: drop useless status masks

These were all copied over from the Blackfin UART driver, but they don't
make sense here because these bits are all specific to the Blackfin UART.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>