UML: fix hostfs build

/home/bunk/linux/kernel-2.6/git/linux-2.6/fs/hostfs/hostfs_kern.c: In function 'hostfs_show_options':
/home/bunk/linux/kernel-2.6/git/linux-2.6/fs/hostfs/hostfs_kern.c:328: error: dereferencing pointer to incomplete type

We need to include mount.h to get vfsmount.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Reported-by: Adrian Bunk <bunk@stusta.de>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hostfs/hostfs_kern.c

@@ -12,6 +12,7 @@
 #include <linux/pagemap.h>
 #include <linux/statfs.h>
 #include <linux/seq_file.h>
+#include <linux/mount.h>
 #include "hostfs.h"
 #include "init.h"
 #include "kern.h"