tty/synclink: remove leftover bits of non-PCI card support

Since commit 1355cba9 ("tty/synclink: remove ISA support"), the
synlink driver only supports PCI card.  Remove any leftover dead code
to support other cards.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20200727130501.31005-1-hch@lst.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>