block: Don't let locked flag prevent medium load

Commit aea2a33c made bdrv_eject() obey the locked flag.  Correct for
medium eject (eject_flag set), incorrect for medium load (eject_flag
clear).  See MMC-5 Table 341 "Actions for Lock/Unlock/Eject".
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -2771,7 +2771,7 @@ int bdrv_eject(BlockDriverState *bs, int eject_flag)
 {
     BlockDriver *drv = bs->drv;
 
-    if (bs->locked) {
+    if (eject_flag && bs->locked) {
         return -EBUSY;
     }