MAINTAINERS: Add file patterns for pinctrl 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>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

MAINTAINERS

@@ -8944,6 +8944,7 @@ M:	Linus Walleij <linus.walleij@linaro.org>
 L:	linux-gpio@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl.git
 S:	Maintained
+F:	Documentation/devicetree/bindings/pinctrl/
 F:	drivers/pinctrl/
 F:	include/linux/pinctrl/