inotify: stop kernel memory leak on file creation failure

If inotify_init is unable to allocate a new file for the new inotify
group we leak the new group.  This patch drops the reference on the
group on file allocation failure.

Reported-by: Vegard Nossum <vegard.nossum@gmail.com>
cc: stable@kernel.org
Signed-off-by: Eric Paris <eparis@redhat.com>