fs/9p/v9fs.c: fix spelling mistake "Uknown" -> "Unknown"

fix spelling mistake in pr_info message text

Link: http://lkml.kernel.org/r/20180526150650.10562-1-colin.king@canonical.com


Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>