watchdog: sprd: Fix the incorrect pointer getting from driver data

commit 39e68d9e upstream.

The device driver data saved the 'struct sprd_wdt' object, it is
incorrect to get 'struct watchdog_device' object from the driver
data, thus fix it.

Fixes: 47760346 ("watchdog: Add Spreadtrum watchdog driver")
Reported-by: Dongwei Wang <dongwei.wang@unisoc.com>
Signed-off-by: Shuiqing Li <shuiqing.li@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/76d4687189ec940baa90cb8d679a8d4c8f02ee80.1573210405.git.baolin.wang@linaro.org


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>