padata: add SPDX identifier

Add SPDX license identifier according to the type of license text found
in the file.

Cc: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/kernel/padata.c b/kernel/padata.c
index 57c0074..d568cc5 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * padata.c - generic interface to process data streams in parallel
  *