iwlwifi: mvm: call a different txq_enable function

Since the SCD_QUEUE_CFG command was introduced the driver
calls iwl_trans_txq_enable_cfg() with a NULL for scd_cfg
parameter.
This makes the transport avoid writing to the SCD pointers,
since it can cause races with firmware, which is also accessing
the registers.
The transport only updates the write pointer in that case.
Fix a wrong call to iwl_trans_txq_enable() which caused a
scd_cfg parameter to be sent to transport, resulting with an
access to SCD registers.

Fixes: 58f2cc57 ("iwlwifi: mvm: support dqa-mode scd queue redirection")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>