fix broken handling of port=... in NFS option parsing

Obviously broken on little-endian; fortunately, the option is not
frequently used...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[ Hey, sparse is wonderful, but even better than sparse is having people
  like Al that actually _run_ it and fix bugs using it.    - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>