staging: vt6656: [BUG] out of bound array reference in RFbSetPower.

Calling RFbSetPower with uCH zero value will cause out of bound array reference.

This causes 64 bit kernels to oops on boot.

Note: Driver does not function on 64 bit kernels and should be
blacklisted on them.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/rf.c

@@ -769,6 +769,9 @@ BYTE    byPwr = pDevice->byCCKPwr;
         return TRUE;
     }
 
+	if (uCH == 0)
+		return -EINVAL;
+
     switch (uRATE) {
     case RATE_1M:
     case RATE_2M: