Staging: p9auth: fix up sparse warnings

Everything needs to be static, as sparse complains and you don't want to
polute the global kernel symbol namespace.  So mark everything as such
and move one function around to prevent a forward declaration from being
needed.

Cc: Ashwin Ganti <ashwin.ganti@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>