rtl8192cu: Prevent Ooops under rtl92c_set_fw_rsvdpagepkt

rtl92c_set_fw_rsvdpagepkt is used by rtl8192cu and its pci sibling rtl8192ce.
rtl_cmd_send_packet crashes when called inside rtl8192cu because it works on
memory allocated only by rtl8192ce.
Fix the crash by calling a dummy function when used in rtl8192cu.
Comparision with the realtek vendor driver makes me think, something is missing in
the dummy function.
Short test as WPA2 station show good results connected to an 802.11g basestation.
Traffic stops after few MBytes as WPA2 station connected to an 802.11n basestation.

Signed-off-by: Karsten Wiese <fzuuzf@googlemail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>