iwlwifi: retfactor get_temperature functions

This patch renames iwl4965_get_tempearture to iwl4965_hw_get_temperature
and replaces usage of original iwl4965_hw_get_temperature by
direct access to priv->temperature.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>