watchdog: orion: Remove unneeded atomic access

The RSTOUT register on the Armada 370 SoC variant is a dedicated register
(not shared across orthogonal subsystems) and so it's not needed to write
it atomically.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Tested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>