ath11k: mhi: add error handling for suspend and resume

While reviewing the mhi.c I noticed we were just ignoring the errors coming
from MHI subsystem during suspend and resume. Add proper checks and warning
messages. Also pass the error value to callers.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03003-QCAHSPSWPL_V1_V2_SILICONZ_LITE-2

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220401173042.17467-3-kvalo@kernel.org