8250: fix break handling for Intel 82571

Intel 82571 has a "Serial Over LAN" feature that doesn't properly
implements the receiving of break characters.  When a break is received,
it doesn't set UART_LSR_DR and unless another character is received, the
break won't be received by the application.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>