freevxfs: Add missing lock_kernel() to vxfs_readdir

Commit 7b2fd697427e73c81d5fa659efd91bd07d303b0e in the historical GIT tree
stopped calling the readdir member of a file_operations struct with the big
kernel lock held, and fixed up all the readdir functions to do their own
locking.  However, that change added calls to unlock_kernel() in
vxfs_readdir, but no call to lock_kernel().  Fix this by adding a call to
lock_kernel().
Signed-off-by: Josh Triplett <josh@freedesktop.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

fs/freevxfs/vxfs_lookup.c

@@ -246,6 +246,8 @@ vxfs_readdir(struct file *fp, void *retp, filldir_t filler)
 	u_long			page, npages, block, pblocks, nblocks, offset;
 	loff_t			pos;
 
+	lock_kernel();
+
 	switch ((long)fp->f_pos) {
 	case 0:
 		if (filler(retp, ".", 1, fp->f_pos, ip->i_ino, DT_DIR) < 0)