dm cache: fix missing return in invalidate_committed's error path

In passthrough mode, dm-cache defers write submission until after
metadata commit completes via the invalidate_committed() continuation.
On commit error, invalidate_committed() calls invalidate_complete() to
end the bio and free the migration struct, after which it should return
immediately.

The patch 4ca8b8bd952d ("dm cache: fix write hang in passthrough mode")
omitted this early return, causing execution to fall through into the
success path on error. This results in use-after-free on the migration
struct in the subsequent calls.

Fix by adding the missing return after the invalidate_complete() call.

Fixes: 4ca8b8bd952d ("dm cache: fix write hang in passthrough mode")
Reported-by: Dan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/dm-devel/adjMq6T5RRjv_uxM@stanley.mountain/
Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>