wil6210: fix check for FW responsiveness

"echo" used to be called when no firmware loaded to the NIC,
this causes error output.

Probe firmware with "echo" only after it returned "ready" event.

Change-Id: I4e1abde313ad73cf9b96c2820436ea9149dd0947
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Git-commit: cec94d8cf5c2e5347ed9264cc94210e6376c7a46
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-testing.git


Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>