freezer: clean up freeze_processes() failure path

freezer: clean up freeze_processes() failure path

freeze_processes() failure path is rather messy.  Freezing is canceled
for workqueues and tasks which aren't frozen yet but frozen tasks are
left alone and should be thawed by the caller and of course some
callers (xen and kexec) didn't do it.

This patch updates __thaw_task() to handle cancelation correctly and
makes thaw_processes() call thaw_processes() on failure instead so
that the system is fully thawed on failure.  Unnecessary
thaw_processes() calls are removed from kernel/power/hibernate.c and
user.c.

Signed-off-by: Tejun Heo <tj@kernel.org>