fs/9p/v9fs.c: add __init to v9fs_sysfs_init

v9fs_sysfs_init is only called by __init init_v9fs

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>