iwlwifi: remove reset led_tpt from iwl_leds_init()

Current blinking rate is calculated based on the difference between
current tx/rx byte counts and priv->led_tpt.

priv->led_tpt should not get reset in iwl_leds_init(), this function can be
called by bring interface "up" or "down", or when uCode sysassert occurred.
resetting the led_tpt parameter will introduce incorrect led blinking behavior.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>