doc: fix gen_devicetree_rest.py bindings search
doc: fix gen_devicetree_rest.py bindings search

The gen_devicetree_rest.py script is responsible for generating .rst
files that comprise the devicetree bindings index. As a first step, it
finds all the YAML files that might be bindings.

However, it's doing that incorrectly and ignoring files in nested
subdirectories. This affects bindings in places like
dts/bindings/net/wireless, which are not found.

Fix it by using recursive=True in the glob.glob() call.

Signed-off-by: Martí Bolívar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@nordicsemi.no>

zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr