watchdog: qcom: Check for platform_get_resource() failure

platform_get_resource() may fail, so we should better check its
return value and propagate an error in case it fails.

This avoids a NULL pointer dereference a bit later in the code.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>