Fix qualified import of Data.Map in QC.hs

As opposed to all other places in the code, we imported this as
Data.Map, leaving to longer names. Let's make it similar to the rest
of the code (import qualified Data.Map as Map).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>