xen/arm: Free p2m entry if fail to add it to RB tree

Release the newly allocated p2m entry if we detect a duplicate in the RB
tree.
Signed-off-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

arch/arm/xen/p2m.c

@@ -156,6 +156,7 @@ bool __set_phys_to_machine_multi(unsigned long pfn,
 	rc = xen_add_phys_to_mach_entry(p2m_entry);
 	if (rc < 0) {
 		write_unlock_irqrestore(&p2m_lock, irqflags);
+		kfree(p2m_entry);
 		return false;
 	}
 	write_unlock_irqrestore(&p2m_lock, irqflags);