imx233: fix bootloader

The bootloader must call disk_init_subsystem() because it is multithread
(because of USB), otherwise strange things might happen. Calling disk_init()
is unnecessary since it is call when mounting partitions.

Change-Id: If7aff3dea0b96144e2a9b0f6179a9a0a632b93ed
diff --git a/bootloader/imx233.c b/bootloader/imx233.c
index 75834c3..6f07d1f 100644
--- a/bootloader/imx233.c
+++ b/bootloader/imx233.c
@@ -176,8 +176,7 @@
 
     /* NOTE: allow disk_init and disk_mount_all to fail since we can do USB after.
      * We need this order to determine the correct logical sector size */
-    while(!disk_init(IF_MV(0)))
-        printf("disk_init failed!");
+    disk_init_subsystem();
 
     if((ret = disk_mount_all()) <= 0)
         error(EDISK, ret, false);