serial: bfin_5xx: remove redundant SSYNC to improve TX speed

We don't need to force a SSYNC here as the LSR register will already
be updated by the time we get back to reading it.  This speeds up TX
throughput and lowers general system overhead (since SSYNC is system
wide, not peripheral-specific).

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>