term/serial: Improve detection of duplicate serial ports

We currently rely on some pretty fragile comparison by name to
identify whether a serial port being configured is identical

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/term/ns8250.c

@@ -364,6 +364,14 @@ grub_serial_ns8250_add_port (grub_port_t port, struct grub_serial_config *config
 	return &com_ports[i];
       }
 
+  FOR_SERIAL_PORTS (p)
+    if (p->mmio == false && p->port == port)
+      {
+        if (config != NULL)
+          grub_serial_port_configure (p, config);
+        return p;
+      }
+
   grub_outb (0x5a, port + UART_SR);
   if (grub_inb (port + UART_SR) != 0x5a)
     return NULL;
@@ -409,6 +417,14 @@ grub_serial_ns8250_add_mmio (grub_addr_t addr, unsigned int acc_size,
         return &com_ports[i];
       }
 
+  FOR_SERIAL_PORTS (p)
+    if (p->mmio == true && p->mmio_base == addr)
+      {
+        if (config != NULL)
+          grub_serial_port_configure (p, config);
+        return p;
+      }
+
   p = grub_malloc (sizeof (*p));
   if (p == NULL)
     return NULL;