qemu-iotests: fix 051 on non-PC architectures

qemu-iotests: fix 051 on non-PC architectures

Commit 61de4c68 [block: Remove BDRV_O_CACHE_WB] updated the reference
output for PCs, but neglected to do the same for the generic reference
output file. Fix 051 on all non-PC architectures by applying the same
change to the generic output file.

Fixes: 61de4c68 ("block: Remove BDRV_O_CACHE_WB")
Signed-off-by: Sascha Silbe <[email protected]>
Reviewed-by: Bo Tu <[email protected]>
Message-id: 1459848109[email protected]
Reviewed-by: Max Reitz <[email protected]>
Signed-off-by: Max Reitz <[email protected]>