PNP: add missing include/linux/pnp.h to MAINTAINERS

include/linux/pnp.h should be covered by the PNP entry in MAINTAINERS,
so add it in there.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -13349,6 +13349,7 @@ F:	Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
 PNP SUPPORT
 M:	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
 S:	Maintained
+F:	include/linux/pnp.h
 F:	drivers/pnp/
 
 POSIX CLOCKS and TIMERS