The temperature variable is set but not used in
iwl_mvm_handle_statistics().  Remove it to avoid the following
compiler warning when W=1 is used:

/home/luca/iwlwifi/stack-dev/drivers/net/wireless/intel/iwlwifi/mvm/rx.c: In function ‘iwl_mvm_handle_rx_statistics’:
/home/luca/iwlwifi/stack-dev/drivers/net/wireless/intel/iwlwifi/mvm/rx.c:759:6: warning: variable ‘temperature’ set but not used [-Wunused-but-set-variable]
  u32 temperature;
      ^
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>