locking: sanlock: Avoid use of VIR_ALLOC_VAR for 'struct sanlk_resource'

locking: sanlock: Avoid use of VIR_ALLOC_VAR for 'struct sanlk_resource'

In both cases we need memory for a 'struct sanlk_resource' followed by
one 'struct sanlk_disk', thus there's no risk of overflow.

Use g_malloc0 and sizeof() to allocate the memory instead of
VIR_ALLOC_VAR.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>