ice: Update ICE_PHY_TYPE_HIGH_MAX_INDEX value

As currently, we are supporting only 5 PHY_SPEEDs for phy_type_high.
Thus, we should adjust the value of ICE_PHY_TYPE_HIGH_MAX_INDEX to 5.

Signed-off-by: Chinh T Cao <chinh.t.cao@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>