ext4: fix NULL pointer dereference in print_daily_error_info()

ext4: fix NULL pointer dereference in print_daily_error_info()

commit a1c6c5698d53db4c47a25c3a8d11731a4d7b8370 upstream.

Fix NULL pointer dereference in print_daily_error_info, when
called on unmounted fs (EXT4_SB(sb) returns NULL), by removing error
reporting timer in ext4_put_super.

Google-Bug-Id: 3017663

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>