The 'needs_rec' parameter for one of the two rdo_mode_decision() calls by
topdown parition search has been passed with wrong value.
It should be false, since re-encoding step follows once rdo_mode_decision()
decided the mode.
In fact, we don't need 'needs_rec' parameter in rdo_mode_decision(), so remove it.

This patch will cause loss of coding efficiency (0.1250% at speed 1)
with a small speedup.

However, if there is more than one intra prediction blocks in a
partition, i.e. tx_size < partition size, rdo_mode_decision() will need
generate reconstrtucted pixels for intra prediction modes. Sine tx
partition is not provided by rav1e yet, this condition can be
implemented in the future.