MAINTAINERS: Fix the link to ad7606 dt-bindings

The devicetree bindings documentation for ad7606 should also include
the vendor prefix: ad7606.txt -> adi,ad7606.txt

Fixes: 6e33a125 ("dt-bindings: iio: adc: Add docs for AD7606 ADC")
Signed-off-by: Stefan Popa <stefan.popa@analog.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -868,7 +868,7 @@ L:	linux-iio@vger.kernel.org
 W:	http://ez.analog.com/community/linux-device-drivers
 S:	Supported
 F:	drivers/iio/adc/ad7606.c
-F:	Documentation/devicetree/bindings/iio/adc/ad7606.txt
+F:	Documentation/devicetree/bindings/iio/adc/adi,ad7606.txt
 
 ANALOG DEVICES INC AD7768-1 DRIVER
 M:	Stefan Popa <stefan.popa@analog.com>