watchdog: ts72xx_wdt: Kill superfluous variable in remove

There is no need to store the return value of misc_deregister() in a
variable. Instead we can just return the value directly.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>