media: i2c: imx355: silence unused acpi_device_id warning

If driver is built without ACPI, the struct acpi_device_id won't be
used:

drivers/media/i2c/imx355.c:1836:36: warning:
'imx355_acpi_ids' defined but not used [-Wunused-const-variable=]

[Sakari Ailus: Added a space before __maybe_unused]

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/i2c/imx355.c

···
 	SET_SYSTEM_SLEEP_PM_OPS(imx355_suspend, imx355_resume)
 };
 
-static const struct acpi_device_id imx355_acpi_ids[] = {
+static const struct acpi_device_id imx355_acpi_ids[] __maybe_unused = {
 	{ "SONY355A" },
 	{ /* sentinel */ }
 };