qapi/machine.json: Fix incorrect description for die-id

In terms of scope, die-id should mean "the die number within
socket the CPU belongs to" instead of "the die number within
node/board the CPU belongs to". Fix it to avoid confusing
the Doc reader.

Fixes: 176d2cda0d ("i386/cpu: Consolidate die-id validity in smp context")
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20211122032651.16064-1-wangyanan55@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qapi/machine.json

@@ -867,7 +867,7 @@
 #
 # @node-id: NUMA node ID the CPU belongs to
 # @socket-id: socket number within node/board the CPU belongs to
-# @die-id: die number within node/board the CPU belongs to (Since 4.1)
+# @die-id: die number within socket the CPU belongs to (since 4.1)
 # @core-id: core number within die the CPU belongs to
 # @thread-id: thread number within core the CPU belongs to
 #