x86/cpu: Fix #define name for Intel CPU model 0x5A

This CPU was mistakenly given the name INTEL_ATOM_AIRMONT_MID. But it
uses a Silvermont core, not Airmont.

Change #define name to INTEL_ATOM_SILVERMONT_MID2

Reported-by: Christian Ludloff <ludloff@gmail.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20241007165701.19693-1-tony.luck%40intel.com