serial: bfin_sport_uart: restore transmit frame sync fix

The large cleanup/rewrite of resources in commit ccf68e59
accidentally reverted an earlier fix in commit a19e8b20.
So restore it here.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: stable <stable@kernel.org> [.34 and newer]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>