fs/9p: fix warnings found by checkpatch.pl

Link: http://lkml.kernel.org/r/20211001063444.102330-1-sohaib.amhmd@gmail.com
Signed-off-by: Sohaib Mohamed <sohaib.amhmd@gmail.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
[Dominique: Fix the fixed indentation...]