ext3: fix a bug accessing freed memory in ext3_abort

Vegard Nossum reported a bug which accesses freed memory (found via
kmemcheck).  When journal has been aborted, ext3_put_super() calls
ext3_abort() after freeing the journal_t object, and then ext3_abort()
accesses it.  This patch fix it.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>