udf: Silence warning about accesses beyond end of device

Some of the computed positions of anchor block could be beyond the end of
device. Skip reading such blocks.

Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/super.c b/fs/udf/super.c
index b9e719d..28ed3f5 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -688,8 +688,12 @@
 	uint16_t ident;
 	uint32_t location;
 
-	if (varconv)
+	if (varconv) {
+		if (udf_fixed_to_variable(block) >=
+		    sb->s_bdev->bd_inode->i_size >> sb->s_blocksize_bits)
+			return 0;
 		bh = sb_bread(sb, udf_fixed_to_variable(block));
+	}
 	else
 		bh = sb_bread(sb, block);