staging: vt6655: dpc.h: Fix comment style of SPDX License Identifier

Modify comment style of SPDX License Identifier for header file type, as
per the license identifier syntax.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>