fs/super.c: fix WARN on alloc_super() fail path

On fail path alloc_super() calls destroy_super(), which issues a warning
if the sb's s_mounts list is not empty, in particular if it has not been
initialized.  That said s_mounts must be initialized in alloc_super()
before any possible failure, but currently it is initialized close to
the end of the function leading to a useless warning dumped to log if
either percpu_counter_init() or list_lru_init() fails.  Let's fix this.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>