fs: dcache reduce branches in lookup path

Reduce some branches and memory accesses in dcache lookup by adding dentry
flags to indicate common d_ops are set, rather than having to check them.
This saves a pointer memory access (dentry->d_op) in common path lookup
situations, and saves another pointer load and branch in cases where we
have d_op but not the particular operation.

Patched with:

git grep -E '[.>]([[:space:]])*d_op([[:space:]])*=' | xargs sed -e 's/\([^\t ]*\)->d_op = \(.*\);/d_set_d_op(\1, \2);/' -e 's/\([^\t ]*\)\.d_op = \(.*\);/d_set_d_op(\&\1, \2);/' -i

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index ef4ee57..0bef62a 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -434,7 +434,7 @@
 	if (!sb->s_root)
 		goto bail_iput;
 
-	sb->s_root->d_op = &hfs_dentry_operations;
+	d_set_d_op(sb->s_root, &hfs_dentry_operations);
 
 	/* everything's okay */
 	return 0;