percpu: stop leaking bitmap metadata blocks

The commit ca460b3c ("percpu: introduce bitmap metadata blocks")
introduced bitmap metadata blocks. These metadata blocks are allocated
whenever a new chunk is created, but they are never freed. Fix it.

Fixes: ca460b3c ("percpu: introduce bitmap metadata blocks")
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dennis Zhou <dennis@kernel.org>