gpio: gpio-mlxbf: Tell the compiler that ACPI functions may not be used

... as is the case when !CONFIG_ACPI.

Fixes the following W=1 kernel build warning:

drivers/gpio/gpio-mlxbf.c:130:36: warning: ‘mlxbf_gpio_acpi_match’ defined but not used [-Wunused-const-variable=]
130 | static const struct acpi_device_id mlxbf_gpio_acpi_match[] = {
| ^~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Lee Jones <[e-mail]>
Cc: Shravan Kumar Ramani <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-mlxbf.c

···
 }
 #endif
 
-static const struct acpi_device_id mlxbf_gpio_acpi_match[] = {
+static const struct acpi_device_id __maybe_unused mlxbf_gpio_acpi_match[] = {
 	{ "MLNXBF02", 0 },
 	{}
 };