Revert "char: moxa, prevent opening unavailable ports"

This reverts commit a90b0375, which
already got fixed as commit f0e85277:
the same patch (trivial differences) got applied twice.

Requested-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>