MAINTAINERS: Add file patterns for w1 device tree bindings

Submitters of device tree binding documentation may forget to CC
the subsystem maintainer if this is missing.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -15394,6 +15394,7 @@ F:	drivers/mmc/host/vub300.c
 W1 DALLAS'S 1-WIRE BUS
 M:	Evgeniy Polyakov <zbr@ioremap.net>
 S:	Maintained
+F:	Documentation/devicetree/bindings/w1/
 F:	Documentation/w1/
 F:	drivers/w1/
 F:	include/linux/w1.h