Staging: kpc2000: kpc_dma: Use the SPDK comment style.

SPDK-License-Identifier comment should have this form
// SPDX-License-Identifier: <GPL-...>
Signed-off-by: Sam Muhammed <jane.pnx9@gmail.com>
Link: https://lore.kernel.org/r/7531e3e3fa7c046e93d2caaa6fa2e76c5c53f04d.1585143581.git.jane.pnx9@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/kpc2000/kpc_dma/dma.c

-/* SPDX-License-Identifier: GPL-2.0+ */
+// SPDX-License-Identifier: GPL-2.0+
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/types.h>

drivers/staging/kpc2000/kpc_dma/fileops.c

-/* SPDX-License-Identifier: GPL-2.0+ */
+// SPDX-License-Identifier: GPL-2.0+
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/mm.h>

drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c

-/* SPDX-License-Identifier: GPL-2.0+ */
+// SPDX-License-Identifier: GPL-2.0+
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/types.h>