Advance submodule head for sonic-utilities

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

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