Fix serial port flushing code.

debug_serial() was doing a full flush while debug_serial_flush() was
only doing a partial flush.  Fix that.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/src/output.c b/src/output.c
index 5c91ae5..462ffb7 100644
--- a/src/output.c
+++ b/src/output.c
@@ -49,7 +49,7 @@
     if (!CONFIG_DEBUG_SERIAL)
         return;
     int timeout = DEBUG_TIMEOUT;
-    while ((inb(CONFIG_DEBUG_SERIAL_PORT+SEROFF_LSR) & 0x60) != 0x60)
+    while ((inb(CONFIG_DEBUG_SERIAL_PORT+SEROFF_LSR) & 0x20) != 0x20)
         if (!timeout--)
             // Ran out of time.
             return;
@@ -63,7 +63,7 @@
     if (!CONFIG_DEBUG_SERIAL)
         return;
     int timeout = DEBUG_TIMEOUT;
-    while ((inb(CONFIG_DEBUG_SERIAL_PORT+SEROFF_LSR) & 0x40) != 0x40)
+    while ((inb(CONFIG_DEBUG_SERIAL_PORT+SEROFF_LSR) & 0x60) != 0x60)
         if (!timeout--)
             // Ran out of time.
             return;