Revert "char: moxa, prevent opening unavailable ports"

This reverts commit a90b037583d5f1ae3e54e9c687c79df82d1d34a4, which
already got fixed as commit f0e8527726b9e56649b9eafde3bc0fbc4dd2dd47:
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>