x86/xen: Convert to DEFINE_SHOW_ATTRIBUTE

Use DEFINE_SHOW_ATTRIBUTE macro to simplify the code.
Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20200917125547.104472-1-miaoqinglang@huawei.comSigned-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/p2m.c

@@ -795,17 +795,7 @@ static int p2m_dump_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static int p2m_dump_open(struct inode *inode, struct file *filp)
-{
-	return single_open(filp, p2m_dump_show, NULL);
-}
-
-static const struct file_operations p2m_dump_fops = {
-	.open		= p2m_dump_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(p2m_dump);
 
 static struct dentry *d_mmu_debug;