staging: r8188eu: Adjust RX gain

In some circumstances, the performance of this driver is highly degraded,
and ifconfig reports large numbers of dropped packets. By increasing the
maximum RX gain from 0x3e to 0x4e, performance is greatly improved.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>