device: Constify struct device * parameter to acpi_fill_ssdt()

.acpi_fill_ssdt() does not need to modify the device structure. This
change makes the struct device * parameter to acpi_fill_ssdt() as
const.

Change-Id: I110f4c67c3b6671c9ac0a82e02609902a8ee5d5c
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40710
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/ec/google/chromeec/ec.h

@@ -344,7 +344,7 @@ int google_chromeec_get_keybd_config(struct ec_response_keybd_config *keybd);
  *
  * @param dev			EC device
  */
-void google_chromeec_fill_ssdt_generator(struct device *dev);
+void google_chromeec_fill_ssdt_generator(const struct device *dev);
 
 /**
  * Returns the ACPI name for the EC device.