rtlwifi: rtl8192c: Update dynamic gain calculations

The vendor driver contained a number of improvements in the gain settings
for the rtl8192c{e,u} devices. This patch implements them in the kernel
driver.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>