qcacmn: Do not print DFS error message for 2.4 GHz pdev
For a 2.4 GHz pdev, dfs object is NULL and hence 'dfs is NULL' print is
in tgt_dfs_set_agile_precac_state().
To fix this, add non 5 GHz pdev check before dfs NULL check.
Change-Id: I32cf622d7b769ce841d30de538527639b87f459b
CRs-Fixed: 2490145