ice: remove unnecessary fallthrough comments

Fallthrough comments are used to explicitly indicate the code is intended
to flow from one case statement to the next in a switch statement rather
than break out of the switch statement.  They are only needed when a case
has one or more statements to execute before falling through to the next
case, not when there is a list of cases for which the same statement(s)
should be executed.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>