iwl4965: fix cannot find a suitable rate issue

This patch fixes the iwl4965 problem for "Can not find a suitable rate
issues." by making rs_switch_to_mimo and rs_switch_to_siso functions
return -1 when CONFIG_IWL4965_HT is not selected. They used to return 0,
which means we can switch to HT rate causing the rate scale problem and
the error message.

The patch also fix another bug reported by Ben Cahill that it uses wrong
value for max_success_limit.

Signed-off-by: Mohamed Abbas <mabbas@linux.intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>