ext4: use ERR_PTR() abstraction for ext4_append()

Use ERR_PTR()/IS_ERR() abstraction instead of passing in a separate
pointer to an integer for the error code, as a code cleanup.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c4e9177..f4466c3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -707,6 +707,8 @@
 	/* ensure we send some value back into *errp */
 	*errp = 0;
 
+	if (create && err == 0)
+		err = -ENOSPC;	/* should never happen */
 	if (err < 0)
 		*errp = err;
 	if (err <= 0)