wlcore: fix read pointer update

When reading the fw_log structure from the device's memory, we could
race with the firmware updating the actual_buff_size and buff_write_ptr
members of this structure. This would lead to bytes being dropped from
the log.

Fix this by writing back the actual - now fixed - clear_ptr which
reflects where we read up to in the buffer.

This also means that we must not check that the clear_ptr matches the
current write pointer, so remove that check.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/E1lolvi-0003Ri-39@rmk-PC.armlinux.org.uk