xen/arm: domain_vgic_init: Avoid double free on shared_irqs

xen/arm: domain_vgic_init: Avoid double free on shared_irqs

When the function domain_vgic_init is failing to initialize pending_irqs,
it will free shared_irqs. Few call later, domain_vgic_free will be called
an try to free a second time the same variable. This will result to a double
free.

Remove the free in domain_vgic_init and rely on domain_vgic_free to correctly
release the memory.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>