watchdog: max77620_wdt: fix module autoload

If the driver is built as a module, autoload won't work because the module
alias information is not filled. So user-space can't match the registered
device with the corresponding module.

Export the module alias information using the MODULE_DEVICE_TABLE() macro.

Before this patch:

$ $ modinfo drivers/watchdog/max77620_wdt.ko | grep alias
$

After this patch:

modinfo drivers/watchdog/max77620_wdt.ko | grep alias
alias:          platform:max77620-watchdog

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>