icnss: Set FW_DOWN bit early stage in fw crash handler

Right now ICNSS_FW_DOWN flag set in platform driver after
indicating to WLAN Host driver. In some case if ICNSS_UEVENT_FW_DOWN
event to wlan host driver get stuck at same time if WLAN host driver
probe failure happens then in failure path before doing BUG_ON driver
check ICNSS_FW_DOWN with platform driver which never set. this result
into false crash.

To avoid this immediately set ICNSS_FW_DOWN flag in platform driver
before indicating to WLAN host driver.

Change-Id: I26c87feb43b5b3de262661552b8d6842a03cb3b5
Signed-off-by: Hardik Kantilal Patel <hkpatel@codeaurora.org>