Avoid redundant tx_type search
Avoid redundant tx_type search

allow_txk_type doesn't contains all the logic of using pre
assigned tx_type or doing the tx_type search.
Here we use get_tx_type to avoid redundant tx_type search.

Change-Id: I09b6bcc60fbe15f0d78689b22d834f95b62bd99a

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom