staging: rtl8712: remove unused variables

unused variables are removed. These variables were only assigned some
values and after that they were never being used. So they are safe to
be removed , and it has been build tested.

I left a call to r8712_read32(padapter, TCR) and
r8712_read8(padapter, SDIO_HCPWM) .

r8712_read32() and r8712_read8() is ultimately calling usb_read32()
and usb_read8() respectively. and they are again calling
r8712_usbctrl_vendorreq().
this r8712_usbctrl_vendorreq() is communicating through the usb bus
and is sending and receiving the control msg.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>