HID: google: fix unused variable warning under !CONFIG_ACPI

As reported by the kernel test robot, the following warning occurs:

>> drivers/hid/hid-google-hammer.c:261:36: warning: 'cbas_ec_acpi_ids' defined but not used [-Wunused-const-variable=]
261 | static const struct acpi_device_id cbas_ec_acpi_ids[] = {
| ^~~~~~~~~~~~~~~~

The 'cbas_ec_acpi_ids' array is only used when CONFIG_ACPI is enabled.
Wrapping its definition and 'MODULE_DEVICE_TABLE' in '#ifdef CONFIG_ACPI'
prevents a compiler warning when ACPI is disabled.

Fixes: eb1aac4c8744f75 ("HID: google: add support tablet mode switch for Whiskers")
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Yu-Chun Lin <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-google-hammer.c

···
 	mutex_unlock(&cbas_ec_reglock);
 }
 
+#ifdef CONFIG_ACPI
 static const struct acpi_device_id cbas_ec_acpi_ids[] = {
 	{ "GOOG000B", 0 },
 	{ }
 };
 MODULE_DEVICE_TABLE(acpi, cbas_ec_acpi_ids);
+#endif
 
 #ifdef CONFIG_OF
 static const struct of_device_id cbas_ec_of_match[] = {