[PCMCIA] Fix oops in validate_mem when CONFIG_PCMCIA_PROBE=n

If I compile a recent 2.5.x kernel without CONFIG_ISA defined, I get
an oops in validate_mem().  Stack trace contains 0x6b6b6b6 - a clear
sign that freed memory is being accessed.

It's the second validate_mem() in drivers/pcmcia/rsrc_mgr.c - the one
used when CONFIG_PCMCIA_PROBE is not defined.  It turns out the memory
is freed in do_mem_probe() when it's called from validate_mem().

The solution is to use the same trick as in the first validate_mem().
This problem is quite serious and it's not specific to the plx9052
driver. I see it with yenta_socket as well.

drivers/pcmcia/rsrc_mgr.c

@@ -499,14 +499,16 @@ void validate_mem(socket_info_t *s)
 
 void validate_mem(socket_info_t *s)
 {
-    resource_map_t *m;
+    resource_map_t *m, *n;
     static int done = 0;
     
     if (probe_mem && done++ == 0) {
 	down(&rsrc_sem);
-	for (m = mem_db.next; m != &mem_db; m = m->next)
+	for (m = mem_db.next; m != &mem_db; m = n) {
+	    n = m->next;
 	    if (do_mem_probe(m->base, m->num, s))
 		break;
+	}
 	up(&rsrc_sem);
     }
 }