fs: return EPERM on immutable inode

In most cases, EPERM is returned on immutable inode, and there're only a
few places returning EACCES. I noticed this when running LTP on
overlayfs, setxattr03 failed due to unexpected EACCES on immutable
inode.

So converting all EACCES to EPERM on immutable inode.

Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/namei.c b/fs/namei.c
index c386a32..adb0414 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -410,7 +410,7 @@
 		 * Nobody gets write access to an immutable file.
 		 */
 		if (IS_IMMUTABLE(inode))
-			return -EACCES;
+			return -EPERM;
 
 		/*
 		 * Updating mtime will likely cause i_uid and i_gid to be