libata: Fix regression when the NCQ Send and Receive log page is absent

Commit 5d3abf8f ("libata: Fall back to unqueued READ LOG EXT if
the DMA variant fails") allowed us to fall back to the unqueued READ
LOG variant if the queued version failed. However, if the device did
not support the page at all we would end up looping due to a merge
snafu.

Ensure we only take the fallback path once.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>