coda: destroy mutex in put_super()

We can safely destroy vc_mutex at the end of umount process.

Link: http://lkml.kernel.org/r/f436f68908c467c5663bc6a9251b52cd7b95d2a5.1558117389.git.jaharkes@cs.cmu.edu
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Mikko Rapeli <mikko.rapeli@iki.fi>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Zhouyang Jia <jiazhouyang09@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/coda/inode.c

@@ -236,6 +236,7 @@ static void coda_put_super(struct super_block *sb)
 	vcp->vc_sb = NULL;
 	sb->s_fs_info = NULL;
 	mutex_unlock(&vcp->vc_mutex);
+	mutex_destroy(&vcp->vc_mutex);
 
 	pr_info("Bye bye.\n");
 }