tty: 8250: Fix up PX-803/PX-857

The PX-803/PX-857 are variants of each other, add a note.
Additionally fix up the port counts for the card (2, not 1).

Fixes: ef5a03a2

 ("tty: 8250: Add support for Brainboxes PX cards.")
Cc: stable@vger.kernel.org
Signed-off-by: Cameron Williams <cang1@live.co.uk>
Link: https://lore.kernel.org/r/DU0PR02MB789978C8ED872FB4B014E132C4DBA@DU0PR02MB7899.eurprd02.prod.outlook.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>