ata: libata: Change ata_dev_knobble() to return a bool

Change the function ata_dev_knobble() to return a boolean instead of a
u8.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Igor Pylypiv <ipylypiv@google.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>