i40e: avoid disable of interrupt when changing ITR

The call to irq_dynamic_disable was turning off the interrupt completely
when trying to set ITR to 0 (for lowest moderation).  Just remove the
call as setting the values to 0 later in this function will suffice.

Change-ID: I47caf1ecbe65653cf63ec833db93094cd83fd84d
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Patrick Lu <patrick.lu@intel.com>
Tested-By: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>