ata: libata-core: Simplify if condition in ata_dev_revalidate()

Simplify the condition used in ata_dev_revalidate() to not
issue identify commands to port multiplier devices.

Signed-off-by: Yahu Gao <gaoyh12@lenovo.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>