dt-bindings: connector: Improve the english of the initial description

The description lacks a few indefinite articles when reading and as a
result is a bit clunky to read. Introduce a few indefinite articles to
appease the grammar gods.

Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Cc: linux-usb@vger.kernel.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Link: https://lore.kernel.org/r/20191128134358.3880498-3-bryan.odonoghue@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/connector/usb-connector.txt

 USB Connector
 =============
 
-USB connector node represents physical USB connector. It should be
-a child of USB interface controller.
+A USB connector node represents a physical USB connector. It should be
+a child of a USB interface controller.
 
 Required properties:
 - compatible: describes type of the connector, must be one of: