[202012][utilities] Update submodule (#7542)

68ea9efc Add pg-drop script to sonic filesystem (#1583)
b216bf0a Fixing serial number read to get from DB if it is populated (#1580)
fa7230c6 Handle the new db version which mellanox_buffer_migrator isn't interested (#1566)

Signed-off-by: Stephen Sun <stephens@nvidia.com>