eeprom: at24: update the license tag

The current GPL v2.0 or later SPDX tag is 'GPL-2.0-or-later' as defined
at https://spdx.org/licenses/.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/misc/eeprom/at24.c

-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * at24.c - handle most I2C EEPROMs
  *