Staging: vt6656: fix up built-in compilation together with rt2870

Fix this build error:

  drivers/staging/vt6656/built-in.o: In function `rotr1':
  (.text+0x1a878): multiple definition of `rotr1'
  drivers/staging/rt2870/built-in.o:(.text+0x106c2): first defined here
  drivers/staging/vt6656/built-in.o: In function `tkip_sbox':
  (.text+0x1a848): multiple definition of `tkip_sbox'
  drivers/staging/rt2870/built-in.o:(.text+0x10697): first defined here
  drivers/staging/vt6656/built-in.o: In function `xor_32':
  (.text+0x1ec24): multiple definition of `xor_32'
  drivers/staging/rt2870/built-in.o:(.text+0x111c4): first defined here
  drivers/staging/vt6656/built-in.o: In function `xor_128':
  (.text+0x1ec00): multiple definition of `xor_128'
  drivers/staging/rt2870/built-in.o:(.text+0x111dd): first defined here

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>