[PATCH v2 1/2] docs: Fix typo in qemu-nbd -P replacement

[Eric Blake <eblake@redhat.com>]

The suggested replacement for the deprecated 'qemu-nbd -P' referw to
'file.backing.opt' instead of 'file.file.opt'; using the example
verbatim results in:

qemu-nbd: Failed to blk_new_open 'driver=raw,offset=1m,size=100m,file.driver=qcow2,file.backing.driver=file,file.backing.filename=file4': A block device must be specified for "file"

Correct this text, prior to actually finishing the deprecation process.

Fixes: 0ae2d54645eb
Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 qemu-deprecated.texi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
index 0968d37c745a..358eb6deebdc 100644
--- a/qemu-deprecated.texi
+++ b/qemu-deprecated.texi
@@ -335,7 +335,7 @@ top of any other existing blockdev. For example, if partition 1 is

 can be rewritten as:

-@code{qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.backing.driver=file,file.backing.filename=file.qcow2}
+@code{qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.file.driver=file,file.file.filename=file.qcow2}

 Alternatively, the @code{nbdkit} project provides a more powerful
 partition filter on top of its nbd plugin, which can be used to select
-- 
2.24.1