icnss: Reject register_driver request when WLAN FW is down

Reject regsiter_driver request when WLAN FW is already down as
WLAN FW is in a bad state and can't communicate with host driver.

Change-Id: I57ba839101f5c0a361e74060b18b45f87c71634c
CRs-Fixed: 2151726
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>