wil6210: take mem_lock for writing in crash dump collection

On some crash dump cases mem_lock is already taken, error
returns and crash dump copy fails.
In this case wait until mem_lock available instead of failing
the operation.
Also take the mem_lock for writing to prevent other threads from
altering the state of the device while collecting crash dump.

Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>