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

Use '-' instead of '=' in identifier: "GPL-2.0-or-later"
Signed-off-by: NTim Bird <tim.bird@sony.com>
Link: https://lore.kernel.org/r/BYAPR13MB2503FF6412666D29FEAC8DCDFD5B9@BYAPR13MB2503.namprd13.prod.outlook.comSigned-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-gxp.c

-// SPDX-License-Identifier: GPL-2.0=or-later
+// SPDX-License-Identifier: GPL-2.0-or-later
 /* Copyright (C) 2022 Hewlett-Packard Development Company, L.P. */
 
 #include <linux/iopoll.h>