fs/9p: Use an IS_ERR test rather than a NULL test

From: Julien Brunel <[email protected]>

In case of error, the function p9_client_walk returns an ERR pointer, but never returns a NULL pointer. So a NULL test that comes after an IS_ERR test should be deleted.

The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@match_bad_null_test@
expression x, E;
statement S1,S2;
@@
x = p9_client_walk(...)
... when != x = E
* if (x != NULL)
S1 else S2
// </smpl>

---
 fs/9p/vfs_inode.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff -u -p a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
@@ -626,8 +626,7 @@ static struct dentry *v9fs_vfs_lookup(st
 	return NULL;
 
 error:
-	if (fid)
-		p9_client_clunk(fid);
+	p9_client_clunk(fid);
 
 	return ERR_PTR(result);
 }