watchdog: rti-wdt: balance pm runtime enable calls

PM runtime should be disabled in the fail path of probe and when
the driver is removed.

Fixes: 2d63908b

 ("watchdog: Add K3 RTI watchdog support")
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200717132958.14304-5-t-kristo@ti.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>