rtl8192cu: Fix missing firmware load

In commit 3ac5e26a

 entitled
"rtlwifi: rtl8192c-common: Change common firmware routines for addition
of rtl8192se and rtl8192de", the firmware loading code was moved.
Unfortunately, some necessary code was dropped for rtl8192cu.

The dmesg output shows the following:

rtl8192c: Loading firmware file rtlwifi/rtl8192cufw.bin
rtl8192c_common:_rtl92c_fw_free_to_go():<0-0> Polling FW ready fail!! REG_MCUFWDL:0x00000006 .
rtl8192c_common:rtl92c_download_fw():<0-0> Firmware is not ready to run!

In addition, the interface will authenticate and associate, but cannot
transfer data.

This is reported as Kernel Bug #38012.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>