lm32_uart/lm32_juart: use qemu_chr_fe_write_all()

qemu_chr_fe_write() may return EAGAIN. Therefore, use
qemu_chr_fe_write_all().

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/hw/char/lm32_juart.c b/hw/char/lm32_juart.c
index 252fe46..380cb5d 100644
--- a/hw/char/lm32_juart.c
+++ b/hw/char/lm32_juart.c
@@ -75,7 +75,7 @@
 
     s->jtx = jtx;
     if (s->chr) {
-        qemu_chr_fe_write(s->chr, &ch, 1);
+        qemu_chr_fe_write_all(s->chr, &ch, 1);
     }
 }