Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
index 06da66b..336f439 100644
--- a/drivers/md/bcache/debug.c
+++ b/drivers/md/bcache/debug.c
@@ -178,10 +178,9 @@
 	while (size) {
 		struct keybuf_key *w;
 		unsigned int bytes = min(i->bytes, size);
-		int err = copy_to_user(buf, i->buf, bytes);
 
-		if (err)
-			return err;
+		if (copy_to_user(buf, i->buf, bytes))
+			return -EFAULT;
 
 		ret	 += bytes;
 		buf	 += bytes;
@@ -249,11 +248,10 @@
 
 void bch_debug_exit(void)
 {
-	if (!IS_ERR_OR_NULL(bcache_debug))
-		debugfs_remove_recursive(bcache_debug);
+	debugfs_remove_recursive(bcache_debug);
 }
 
-void __init bch_debug_init(struct kobject *kobj)
+void __init bch_debug_init(void)
 {
 	/*
 	 * it is unnecessary to check return value of