xen/pvcalls: free active map buffer on pvcalls_front_free_map

xen/pvcalls: free active map buffer on pvcalls_front_free_map

Data buffer for active map is allocated in alloc_active_ring and freed
in free_active_ring function, which is used only for the error
cleanup. pvcalls_front_release is calling pvcalls_front_free_map which
ends foreign access for this buffer, but doesn't free allocated pages.
Call free_active_ring to clean all allocated resources.

Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/6a762ee32dd655cbb09a4aa0e2307e8919761311.1671531297.git.oleksii_moisieiev@epam.com
Signed-off-by: Juergen Gross <jgross@suse.com>