wifi: wfx: simplify exclusion between scan and Rx filters

The device ignore the rx filters during the scan operation.
wfx_configure_filter() acquires scan_lock to reflect this restriction.
However, it is not really necessary since mac80211 don't try to
configure Rx filters during scan.

However, the things are changing. The scan operation is going to be used
to implement remain-on-channel. In this case, wfx_configure_filter() can
be called during the scan. Currently, this scenario generate a delay
that end with a timeout in the upper layers. For the final user, some
scenario of the EasyConnect specification end with a failure.

So, avoid acquiring the scan_lock and just return.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231004172843.195332-6-jerome.pouiller@silabs.com