char/serial: Fix emptyness check

This was guarding against a full fifo rather than an empty fifo when
popping. Fix.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/char/serial.c

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 27dab7d..6d3b5af 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -225,7 +225,7 @@
 
     if (s->tsr_retry <= 0) {
         if (s->fcr & UART_FCR_FE) {
-            s->tsr = fifo8_is_full(&s->xmit_fifo) ?
+            s->tsr = fifo8_is_empty(&s->xmit_fifo) ?
                         0 : fifo8_pop(&s->xmit_fifo);
             if (!s->xmit_fifo.num) {
                 s->lsr |= UART_LSR_THRE;