staging: vt6655: Fix RFbSetPower() error: buffer overflow 'priv->abyCCKPwrTbl' 15 <= 56

Check uCH is not more than CB_MAX_CHANNEL_24G(14) on rates RATE_1M to RATE_11M

Return false as the call is invalid as these rates do not exist
above channel 14.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>