watchdog: omap: clearify device tree documentation

ti,hwmods doesn't belong into the compatible section but is a property
on it's own. Also reformat the section of required properties to match the
usual style of dt binding documents.
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: NFelipe Balbi <balbi@ti.com>
Acked-by: NFelipe Balbi <balbi@ti.com>
Reviewed-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/omap-wdt.txt

 TI Watchdog Timer (WDT) Controller for OMAP
 
 Required properties:
-compatible:
-- "ti,omap3-wdt" for OMAP3
-- "ti,omap4-wdt" for OMAP4
-- ti,hwmods: Name of the hwmod associated to the WDT
+- compatible : "ti,omap3-wdt" for OMAP3 or "ti,omap4-wdt" for OMAP4
+- ti,hwmods : Name of the hwmod associated to the WDT
 
 Examples: