Input: elan_i2c - extend Flash-Write delay

The original 20ms delay is only marginally enough delay after a block write
operation during firmware update. Let's increase the delay to ensure that
the controller finishes up storing the page to avoid failures in the
firmware updates.

Signed-off-by: KT Liao <kt.liao@emc.com.tw>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>