xen/xenbus: Convert to use ERR_CAST()

Use ERR_CAST() as it is designed for casting an error pointer to
another type.

This macro utilizes the __force and __must_check modifiers, which instruct
the compiler to verify for errors at the locations where it is employed.

Signed-off-by: Shen Lichuan <shenlichuan@vivo.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20240829084710.30312-1-shenlichuan@vivo.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/xenbus/xenbus_xs.c

@@ -427,12 +427,12 @@ char **xenbus_directory(struct xenbus_transaction t,
 
 	path = join(dir, node);
 	if (IS_ERR(path))
-		return (char **)path;
+		return ERR_CAST(path);
 
 	strings = xs_single(t, XS_DIRECTORY, path, &len);
 	kfree(path);
 	if (IS_ERR(strings))
-		return (char **)strings;
+		return ERR_CAST(strings);
 
 	return split(strings, len, num);
 }
@@ -465,7 +465,7 @@ void *xenbus_read(struct xenbus_transaction t,
 
 	path = join(dir, node);
 	if (IS_ERR(path))
-		return (void *)path;
+		return ERR_CAST(path);
 
 	ret = xs_single(t, XS_READ, path, len);
 	kfree(path);