Input: wdt87xx_i2c - fix the flash erase issue

The spec says that flash erase time is 30ms typical/200ms max, so let's
replace current 50ms wait with 200ms to avoid potential failures.

Signed-off-by: HungNien Chen <hn.chen@weidahitech.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>