wil6210: fix beamforming data reporting

When reading 'bf' file on debugfs, query beam forming status from firmware.
Ignore CID's that return error or return all zeros.

Remove obsolete code that used to maintain statistics on per-device basis,
as now it is reported be per-CID and current.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>