ath11k: Fix warning on variable 'sar' dereference before check

We are seeing below warning:
warn: variable dereferenced before check 'sar'

Fix it by moving ahead pointer check on 'sar'.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3

Fixes: 652f69ed ("ath11k: Add support for SAR")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220517004844.2412660-1-quic_bqiang@quicinc.com