MAINTAINERS: Add linux-acpi list to PNP

As asked by the PNP maintainer, linux PNP patch should be CC to
the linux-acpi mailing list.
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -13348,6 +13348,7 @@ F:	Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
 
 PNP SUPPORT
 M:	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
+L:	linux-acpi@vger.kernel.org
 S:	Maintained
 F:	include/linux/pnp.h
 F:	drivers/pnp/