rtlwifi: rtl8192ce: rtl8192cu: rtl8192de: Fix low-gain setting when scanning

In https://bugzilla.redhat.com/show_bug.cgi?id=770207

, slowdowns of driver
rtl8192ce are reported. One fix (commit a9b89e25) has already been applied,
and it helped, but the maximum RX speed would still drop to 1 Mbps. As in
the previous fix, the initial gain was determined to be the problem; however,
the problem arises from a setting of the gain when scans are started.

Driver rtl8192de also has the same code structure - this one is fixed as well.

Reported-and-Tested-by: Ivan Pesin <ivan.pesin@gmail.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>