spi: spi-gxp: fix typo in SPDX identifier line

Use '-' instead of '=' in identifier: "GPL-2.0-or-later"

Signed-off-by: Tim Bird <tim.bird@sony.com>
Link: https://lore.kernel.org/r/BYAPR13MB2503FF6412666D29FEAC8DCDFD5B9@BYAPR13MB2503.namprd13.prod.outlook.com


Signed-off-by: Mark Brown <broonie@kernel.org>