staging: r8712u: Fix regression in signal level after commit c6dc001f

In commit c6dc001f "staging: r8712u: Merging Realtek's latest (v2.6.6).
Various fixes", the returned qual.qual member of the iw_statistics
struct was changed. For strong signals, this change made no difference;
however for medium and weak signals it results in a low signal that
shows considerable fluctuation, When using wicd for a medium-strength
AP, the value reported in the status line is reduced from 100% to 60% by
this bug.

This problem is reported in https://bugzilla.kernel.org/show_bug.cgi?id=42826

.

Reported-and-tested-by: Robert Crawford <wrc1944@gmail.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>