aspeed/wdt: Check correct register for clock source

aspeed/wdt: Check correct register for clock source

When WDT_RESTART is written, the data is not the contents
of the WDT_CTRL register. Hence ensure we are looking at
WDT_CTRL to check if bit WDT_CTRL_1MHZ_CLK is set or not.

Signed-off-by: Amithash Prasad <amithash@fb.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20190925143248.10000-2-clg@kaod.org
[clg: improved Suject prefix ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>