ata: libata-eh: Increase STANDBY IMMEDIATE timeout

ata: libata-eh: Increase STANDBY IMMEDIATE timeout

Correct a previous change (see Fixes) which reduced the standby timeout
from 30 to 5 seconds. Increase it to 15 seconds.

I was troubleshooting an error spotted during system suspend:

    [ 1217.152867] ata1.00: Entering standby power mode
    [ 1222.322948] ata1.00: qc timeout after 5000 msecs (cmd 0xe0)
    [ 1222.324010] ata1.00: STANDBY IMMEDIATE failed (err_mask=0x4)

This drive is a Samsung 870 EVO SSD in good SMART standing, and I wasn't
aware of any reason it should be taking so long to standby. The issue is
intermittent, but I observed it sometimes taking 7 seconds to manually
standby. I assume this was interruption of background maintenance after
a power outage.

As a desktop user, I would prefer to wait the extra 2 seconds at suspend
to let the drive finish its business rather than drop the rails from
under it.

The change from 30 to 5 seconds was implicit when switching suspend
from START STOP UNIT to an internal command with no timeout table entry.
No reason was stated for the change.

Fixes: aa3998dbeb3a ("ata: libata-scsi: Disable scsi device manage_system_start_stop")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Vollrath <tactii@gmail.com>
Assisted-by: Claude:claude-5-fable
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>