By default all files without license information are under the default
license of the kernel, which is GPL version 2.  Because of this, add the
GPL-2.0 identifier to the sm750fb driver which did not have any license
identifiers in it at all.

Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>