jbd2: deregister proc on failure in jbd2_journal_init_inode

jbd2_journal_init_inode() does not call jbd2_stats_proc_exit() on all
failure paths after calling jbd2_stats_proc_init(). This leaves
dangling references to the fs in proc.

This patch fixes a bug reported by Sami Leides at:
http://bugzilla.kernel.org/show_bug.cgi?id=11493

Signed-off-by: Sami Liedes <sliedes@cc.hut.fi>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>