cnss2: Do not send FW_DOWN to WLAN host driver

There is no need to send FW_DOWN to WLAN host driver anymore since
it will query platform driver directly for the status. Also clear
the device error flag after firmware is ready.

Change-Id: I5b488765e85af0cd28a4c10f009f0b7790141f01
Signed-off-by: Yue Ma <yuem@codeaurora.org>