wifi: ath11k: Add missing check for ioremap

Add check for ioremap() and return the error if it fails in order to
guarantee the success of ioremap(), same as in
ath11k_qmi_load_file_target_mem().

Fixes: 6ac04bdc ("ath11k: Use reserved host DDR addresses from DT for PCI devices")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230608022858.27405-1-jiasheng@iscas.ac.cn