Squashfs: use define instead of constant

Its better to use defined name instead of constant

Signed-off-by: Ajeet Yadav <ajeet.yadav.77@gmail.com>
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
diff --git a/fs/squashfs/dir.c b/fs/squashfs/dir.c
index 9dfe2ce..4a812bfc 100644
--- a/fs/squashfs/dir.c
+++ b/fs/squashfs/dir.c
@@ -173,8 +173,7 @@
 
 		dir_count = le32_to_cpu(dirh.count) + 1;
 
-		/* dir_count should never be larger than 256 */
-		if (dir_count > 256)
+		if (dir_count > SQUASHFS_DIR_COUNT)
 			goto failed_read;
 
 		while (dir_count--) {